Nikolai Olavi Czajkowski

• Kraft, Brage; MacSweeney, Niamh Anne; Page, Christian Magnus; Lyle, Robert; Tsotsi, Stella & Ulset, Vidar Sandsaunet [Show all 12 contributors for this article] (2026). The effect of prenatal maternal stress on adolescent internalizing symptoms and the genetic moderation of executive functioning and prefrontal cortex. Psychological Medicine. ISSN 0033-2917. 56. doi: 10.1017/S0033291726105431. Full text in Research Archive Show summary

  Background: Prenatal maternal stress is a known risk factor for later emotional problems, yet not all exposed offspring develop psychopathology. Executive functioning and prefrontal cortex structure and activity may buffer these effects, but it remains unclear whether genetic predis positions in these domains moderate associations with adolescent internalizing symptoms. Methods: We examined 3,111 adolescents (1,881 females, 1,230 males). Prenatal stress was measured via a cumulative index across four domains. Internalizing symptoms were self reported at ages 14 and 16. Genetic predisposition for executive functioning was indexed using a polygenic score (PGS) derived from adult samples, applied here to estimate genetic predis position for executive functioning in adolescence. We also estimated a prefrontal cortex PGS based on cortical thickness and activation in six prefrontal regions, with a composite index derived from the first principal axis summarizing these measures. Results: Higher prenatal stress was significantly associated with more internalizing symptoms in adolescence. Female sex and maternal genetic risk for internalizing symptoms were also associated with higher symptom levels. Neither genetic disposition for executive functioning nor prefrontal cortex moderated this association overall. However, a weak interaction emerged at age 16, indicating that a genetic disposition for higher executive functioning was associated with greater internalizing symptoms under high stress exposure. Conclusions: Prenatal maternal stress predicted increased adolescent internalizing symptoms, with limited evidence for moderation by genetic predisposition for executive functioning. Higher genetic potential for executive functioning may confer increased sensitivity to early stress under certain developmental conditions.

• Walhovd, Kristine B; Bråthen, Anne Cecilie Sjøli; Øverbye, Knut Eiliv Ødegård; Kransberg, Jonas Moe; Sørensen, Øystein & Garrido, Pablo F. [Show all 19 contributors for this article] (2026). Feature-specific environmental contributions to human cortical architecture revealed by twin brainprints. Communications Biology. doi: 10.1038/s42003-026-10707-w. Full text in Research Archive Show summary

  Abstract How environmental variation shapes the human cerebral cortex remains incompletely understood. Here we compare cortical brainprints – individual profiles of regional cortical morphology – in 210 twins (age 16-78 years) to distinguish prenatal, adult naturalistic and experimentally induced environmental variation from genetic contributions. Monozygotic twins showed higher brainprint similarity than dizygotic twins, consistent with genetic effects. Lasting influences of early environment were evident in lower brainprint similarity in monozygotic twin-pairs with greater birthweight discordances, driven by surface area across the cortical ribbon. In contrast, within-pair differences in adult weight and lifestyle had minimal influence. Still, a 10-week virtual-reality navigation intervention revealed training-induced changes in the gray-white interface, with curvature and area changes supported by microstructural reconfigurations. Relative brainprint similarity increased in monozygotic but diverged in dizygotic pairs following training. These findings show that distinct environmental influences acting at prenatal and adult stages are reflected in different features of the human cerebral cortex.

• Eilertsen, Maja; Czajkowski, Nikolai Olavi; Omsland, Tone Kristin; Røysamb, Espen & Nes, Ragnhild Bang (2026). Wellbeing, mastery and work participation: Effects of the Five Ways to Wellbeing course—a randomized controlled trial. Scandinavian Journal of Public Health. ISSN 1403-4948. doi: 10.1177/14034948261479465. Full text in Research Archive Show summary

  Background: Rising ill health, declining wellbeing, and absenteeism threaten societal sustainability amid an ageing population. Promoting health, wellbeing and work participation is essential. The Five Ways to Wellbeing course is a six-week programme designed to enhance wellbeing through five core activities: connecting, being active, taking notice, learning, and giving. A digital, shorter version has shown effectiveness in the general population, but the physical course has not been evaluated by randomized controlled trial in high-risk groups. Methods: This parallel two-group randomized controlled trial examined the effects of the Five Ways to Wellbeing course versus no course. Adults (⩾18 years old) receiving benefits through the Norwegian Labour and Welfare Administration were randomly assigned to the intervention or control group. The trial was non-blinded; participants were aware of group allocation because blinding was not feasible. Main outcomes were wellbeing, mastery and work participation, measured at baseline, post-intervention and six months. Multilevel analyses compared repeated measures across groups. Results: A total of 171 adults were randomized to the intervention (n = 87) or the control group (n = 84). Owing to attrition, data from 71 intervention and 46 control participants were included in the final analyses. No statistically significant differences in wellbeing, mastery or work participation were observed between groups. Conclusions: This underpowered trial found no statistically significant effects, limiting conclusions about the course’s effectiveness. However, it provides insight into the challenges of conducting pragmatic randomized trials within routine welfare services.

• Prydz, Monica Beer; Røysamb, Espen; Czajkowski, Nikolai Olavi & Nes, Ragnhild Bang (2026). The Digital Five Ways to Wellbeing Intervention: Long-Term Change in Life Satisfaction. Applied Research in Quality of Life. ISSN 1871-2584. doi: 10.1007/s11482-026-10628-0. Full text in Research Archive Show summary

  The worldwide burden of mental health problems is substantial. Preventive and promotive interventions with impact on the population level are needed. The Five Ways to Wellbeing is a health-promotive evidence-informed framework that supports the importance of five specific action domains (connect, take notice, be active, keep learning and give). This framework was recently documented to be effective in enhancing wellbeing through a low-dosage digital intervention termed the Five Ways to Wellbeing for All (5waysA). However, the duration of the effects has not been examined. In the present study, we investigate the long-term (12-month) enhancement of life satisfaction following the intervention in a single-group design utilizing multilevel modeling and piecewise regression (n = 731). Subsequently, we simulate the trajectory for a synthetic control group, using Norwegian population data (Mean and SD), to serve as an untreated counterfactual for comparison. For the intervention group, our analysis revealed a significant increase in life satisfaction (SWLS) from baseline to follow-up (12 months) (d = 0.28; p < 0.01). Further analysis including the synthetic population-based control group showed a significant (p < 0.05) between-group difference in wellbeing at 12 months. Cohen’s d effect size for this between group difference was 0.17 (p < 0.05). With low administration costs and high scalability, 5waysA may offer policymakers and practitioners an effective way to promote lasting improvements in wellbeing. Considering the resource demands associated with the use of regular control groups, we also hope to inspire the field to adopt resource-efficient synthetic control methods to study the long-term effects of health interventions.

• Tsotsi, Stella; Coplan, Robert J.; Czajkowski, Nikolai Olavi & Bekkhus, Mona (2026). Co-occurrence of internalizing difficulties and aggression in preschoolers and mental health outcomes in adolescence. International Journal of Behavioral Development. ISSN 0165-0254. doi: 10.1177/01650254261438685. Full text in Research Archive
• Eilertsen, Maja; Czajkowski, Nikolai Olavi; Røysamb, Espen; Omsland, Tone Kristin; Prydz, Monica Beer & Blom, Ellen Eimhjellen [Show all 7 contributors for this article] (2026). Changes in Wellbeing, Social Connection, and Health following Participation in the Five Ways to Wellbeing Course: A Non-Randomized, Longitudinal, Quasi-Experimental Study in Help-Seeking Participants. International Journal of Applied Positive Psychology. ISSN 2364-5040. 11. doi: 10.1007/s41042-025-00271-9. Full text in Research Archive Show summary

  Society faces a growing burden of preventable health-related issues, highlighting the need for effective interventions that promote health and prevent illness, particularly among high-risk groups. The Five Ways to Wellbeing course is a 6-week intervention designed to enhance wellbeing and health by encouraging participants to practice five key activities: connect, be active, take notice, keep learning, and give. This study assessed changes in wellbeing, social connection, and health among participants facing physical and mental health challenges, following participation in the Five Ways to Wellbeing course, using a non-randomized, longitudinal, quasi-experimental design.&nbsp;A total of 373 adults who participated in the Five Ways to Wellbeing course were assessed at baseline, immediately after the intervention, and at 6- and 15-months post-intervention. Wellbeing, social connection, and physical and mental health were measured using validated questionnaires. A non-randomized comparison group (n = 923) from a separate study was included, as randomization was not possible. Changes over time and between groups were analyzed using paired t-tests and multilevel models.&nbsp;Participants reported significant improvements in wellbeing and social connection, sustained at 6 and 15 months (Cohen’s d = 0.21–0.63). Improvements in mental health were greater than in the comparison group, with statistically significant time-by-group interaction effects (p = 0.012 at post-test; p = 0.002 at 15 months). Improvements in physical health were comparable between groups (p = 0.206 and p = 0.107).&nbsp;The Five Ways to Wellbeing course may offer a promising approach to improving short- and long-term wellbeing, social connection, and subjective health in a group of vulnerable participants seeking to improve their health.

• Valstad, Mathias; Eftedal, Nikolai Haahjem; Yang, Tianfang; Kvarstein, Elfrida Hartveit; Reichborn-Kjennerud, Ted & Ystrom, Eivind [Show all 7 contributors for this article] (2026). The epidemiology of personality disorders in Norway: a nationwide patient registry study. Social Psychiatry and Psychiatric Epidemiology. ISSN 0933-7954. doi: 10.1007/s00127-026-03083-7. Full text in Research Archive
• Eftedal, Nikolai Haahjem; Kleppestø, Thomas Haarklau; Czajkowski, Nikolai Olavi; Eilertsen, Espen Moen; Røysamb, Espen & Vassend, Olav Mandt [Show all 8 contributors for this article] (2026). The Relationship Between Educational Attainment and Right-Wing Authoritarianism: A Discordant Twin Study. Personality and Social Psychology Bulletin. ISSN 0146-1672. doi: 10.1177/01461672251407779. Full text in Research Archive
• Liu, Hang; Laeng, Bruno & Czajkowski, Nikolai Olavi (2025). Visual short-term memory is modulated by 3D depth in stereopsis. Attention, Perception & Psychophysics. ISSN 1943-3921. 87(8), p. 2265–2274. doi: 10.3758/s13414-025-03052-3. Full text in Research Archive Show summary

  Visual short-term memory (VSTM) is a memory mechanism temporarily holding visual information for later use. In the real world, objects are located in spatial depth and such depth information may be processed when objects are remembered. The present study investigated how VSTM is modulated by three-dimensional (3D) depth. Previous work used the color of objects to measure memory and provided mixed results, and the impact of separability in depth on memory is unclear. In Experiment 1a, we employed color feature and examined the effect of 3D depth across Stereo (stereoscopic vs. monoscopic) and Plane (one plane vs. multiple planes). VSTM was not found to be influenced by depth information. In Experiments 1b and 1c, the color was respectively replaced with two distinct spatial features, orientation and direction-of-rotation. We found similar results that the performance on VSTM was superior in the stereoscopic multi-plane condition compared to the monoscopic multi-plane condition or stereoscopic single-plane condition. These findings confirm, also via Bayesian statistical analyses, that the VSTM can benefit from 3D depth information in stereopsis, while the benefit is severely limited when the task is non-spatial.

• Eilertsen, Maja; Hansen, Thomas; Torre, Maria Julia Bidonde; Reneflot, Anne; Nilsen, Thomas Sevenius & Czajkowski, Nikolai Olavi [Show all 7 contributors for this article] (2025). Effects of Positive Psychology Interventions on Inflammatory Biomarkers and Cortisol: A Systematic Review and Meta-Analysis. International Journal of Applied Positive Psychology. ISSN 2364-5040. 10(4), p. 1–33. doi: 10.1007/s41042-025-00258-6. Full text in Research Archive Show summary

  Abstract There is growing interest in how well-being-enhancing activities influence stress and health. Positive psychology interventions (PPIs) foster such activities, but evidence regarding their physiological effects remains fragmented. This review aimed to examine the effects of PPIs on two physiological indicators of stress via a systematic literature review and meta-analysis. We included randomized controlled trials (RCTs) assessing the effects of PPIs on inflammatory biomarkers and/or cortisol in adult clinical and non-clinical populations. Searches were conducted in MEDLINE, Embase, PsycINFO, Epistemonikos, and clinical trial registries (from January 2000 to June 2023). Two reviewers independently screened studies, extracted data, and assessed risk of bias. Random-effects meta-analyses using robust variance estimation accounted for statistical dependencies. Effects were reported as Cohen’s d with 95% confidence intervals (CIs) and heterogeneity as prediction intervals (PIs). Twenty-five RCTs ( N  = 1,641) were included. Common PPIs included music, nature exposure, gratitude, optimism, kindness, and meaning-focused activities. The overall effect was d  = 0.39 (95% CI: 0.16, 0.62). The effect estimates were significant for inflammatory biomarkers ( d  = 0.46, 95% CI: 0.02, 0.89), but not for cortisol ( d  = 0.30, 95% CI: − 0.10, 0.71). A significant effect was observed in clinical groups ( d  = 0.61, 95% CI: 0.17, 1.04); the effect in non-clinical groups was non-significant ( d  = 0.23, 95% CI: − 0.01, 0.79). High heterogeneity and risk of bias warrant cautious interpretation. These findings suggest that PPIs may reduce inflammatory biomarkers. The clinical relevance of these effects remains uncertain and warrants further investigation, particularly in relation to long-term outcomes. Registration : The study protocol was registered with PROSPERO (CRD42023438736).

• Hofgaard, Live Skow; Nes, Ragnhild Bang; Vassend, Olav Mandt; Ayorech, Ziada; Czajkowski, Nikolai Olavi & Røysamb, Espen (2025). Mental illbeing and wellbeing are influenced by recent adverse life events. Evidence from a longitudinal twin study. Current Psychology. ISSN 1046-1310. 44, p. 8723–8735. doi: 10.1007/s12144-025-07758-3. Full text in Research Archive Show summary

  Adverse life events have been associated with increased mental illbeing and decreased wellbeing. These associations may partly reflect reverse causality and confounding genetics. Few studies have accounted for such effects, and few have compared the effect of adversities within and across different mental health outcomes. Our sample includes 1987 monozygotic and dizygotic twins born 1945-60, in the Norwegian Twin Registry, who responded to two questionnaires six years apart. We used biometric modelling to estimate genetic overlap and linear mixed models to control for previous levels of illbeing and wellbeing as well as genetic confounding in the associations between adverse life events and these outcomes. Our results indicate causal effects of cumulative adversity on increased illbeing and decreased wellbeing. Of the six adversities examined separately, financial strain and conflicts in romantic relationships showed the most profound effect on both outcomes. Conflicts with family/friends/neighbours and problems at work seem to primarily increase illbeing, while serious illness or injury mainly decrease wellbeing. This study supports previous findings that cumulative adversity represents a risk for increased illbeing and decreased wellbeing. Hence, exploring the number of recent adverse events could give valuable insight into individuals’ stressor load, and the reduction and prevention of such events should be important targets for preventive programs and policy. Importantly, our findings further suggest that the events that increase illbeing are not always overlapping with those that decrease wellbeing. This should be taken into consideration when assessing the needs of individuals after difficult experiences.

• Høstmælingen, Andreas Teisner; Nissen-Lie, Helene, Amundsen; Monsen, Jon Trygve; Heinonen, Erkki; Wampold, Bruce E. & Czajkowski, Nikolai Olavi [Show all 9 contributors for this article] (2025). Use of antidepressant medication is associated with slower response to open-ended psychotherapy for depressed patients. Frontiers in Psychiatry. 16. doi: 10.3389/fpsyt.2025.1503848. Full text in Research Archive Show summary

  Objective Depressed patients often experience both symptomatic distress and interpersonal problems. Comorbid personality disorder (PD) has been shown to attenuate the benefits of psychotherapy. Also, antidepressant medication (ADM) may affect the response to psychotherapy. The objective of this study was to investigate changes in depressive symptoms and interpersonal problems for ADM users and non-medicated depressed patients during psychotherapy and follow-up, controlling for comorbid PD. Method Depressive symptoms (SCL-90-R), and interpersonal problems (IIP-64) were assessed on 11 occasions for 166 depressed patients. ADM was used by 50.6% of the sample while 49.4% were unmedicated. Change during treatment and follow-up was assessed with multilevel modeling. We assessed whether ADM and PD predicted differences in symptom development. Results Depressive symptoms significantly reduced at a rate of.05 per month in treatment ( p &lt;.001), corresponding to an effect size of 1.35. Interpersonal problems significantly reduced at a rate of.02 per month during treatment ( p &lt;.001), corresponding to an effect size of.47. There was no significant difference between ADM users and nonmedicated patients at baseline. ADM users had nearly twice as long treatment duration than nonmedicated patients, and ADM users had lower rate of symptom reduction than nonmedicated patients for depressive symptoms and interpersonal problems. There were no differences in rates of change between patients with and without comorbid PD. Conclusion Medicated patients may experience less response to psychotherapy in terms of depressive symptoms and interpersonal problems compared to nonmedicated patients.

• Prydz, Monica Beer; Bjørndal, Ludvig Daae; Czajkowski, Nikolai Olavi; Røysamb, Espen & Nes, Ragnhild Bang (2025). Direct and indirect effects of a digital Five Ways to Wellbeing intervention: A network intervention analysis. Behaviour Research and Therapy. ISSN 0005-7967. 191. doi: 10.1016/j.brat.2025.104781. Full text in Research Archive Show summary

  While digital positive psychology interventions demonstrate effectiveness in promoting wellbeing and reducing illbeing in the general population, their pathways of change are relatively underexplored. The wellbeing promotive digital intervention, Five Ways to Wellbeing for All (5waysA), has been shown effective (Cohens’ d effect sizes from .20 to .49) in a large (N = 963) randomized controlled trial (Prydz et al., 2024). In the present study, network intervention analysis (NIA) was applied to identify putative direct and indirect effects linking the 5waysA intervention to a set of wellbeing outcomes. Following the 10-week intervention period, the NIA revealed that only positive emotions on an aggregate level were conditionally dependent on the treatment allocation variable. These findings suggest that the effectiveness of the 5waysA intervention primarily reflects the direct enhancement of positive emotions. Our findings provide insights of potential importance for advancing the theoretical framework of the Five Ways to Wellbeing and other mental health and wellbeing promoting interventions.

• Hansen, Heidi Marie Umbach; Røysamb, Espen; Vassend, Olav Mandt; Czajkowski, Nikolai Olavi; Endestad, Tor & Vuoskoski, Jonna Katariina [Show all 8 contributors for this article] (2025). Dimensions of music use motivations: Genetic and environmental underpinnings, and associations with Big Five and Empathy traits. PLOS ONE. 20(8). doi: 10.1371/journal.pone.0329808. Full text in Research Archive Show summary

  People differ in their motivation for seeking musical experiences and these differences appear to be partially attributable to their personality. However, little is known about the role of genetic and environmental factors in shaping individual differences in motivations for music use and their shared etiology with personality. This study investigated, using the classical twin design in a sample of 2611 Norwegian twins, the genetic and environmental architecture of four dimensions of motivations for music use (musical transcendence, emotion regulation, social bonding, and musical identity and expression). We also examined their phenotypic associations, as well as genetic and environmental overlap with general personality traits, including the Big Five and Trait Empathy facets. Additive genetic and unique environmental effects largely accounted for the variation in the four dimensions (heritability 38%−52%, mean = 45%), though univariate analyses of the social bonding dimension indicated common environmental influences for this specific subscale. In line with previous studies, trait-congruent phenotypic associations were found between specific personality traits and music use motives, including facets of negative emotionality and musical emotion regulation. Other facets – particularly aesthetic sensitivity (open-mindedness) and fantasy (trait empathy) – were closely tied to all dimensions. Multivariate biometric modeling of the links between personality traits and motivations for music use revealed that these relationships were primarily driven by correlated genetic factors, with personality traits accounting for 40%−66% of the total genetic variance and 5%−17% of the total environmental variance in the music use motivation dimensions. These findings shed new light on the etiology of dispositional music use and provide a comprehensive baseline for future investigations of associations with personality, mental health, and well-being.

• Eftedal, Nikolai Haahjem; Eilertsen, Espen Moen; Sunde, Hans Fredrik; Kleppestø, Thomas Haarklau; Ystrøm, Eivind & Czajkowski, Nikolai Olavi (2025). Beyond additive genetic effects: Explaining family resemblance in school performance across millions of pairs of Norwegian relatives. Proceedings of the National Academy of Sciences of the United States of America (PNAS). ISSN 0027-8424. 122(25), p. 1–9. doi: 10.1073/pnas.2419627122. Full text in Research Archive Show summary

  We investigate the hypothesis that family resemblance on school performance can be fully explained by additive genetic effects and assortative mating. Our sample consists of all schoolchildren who took Norwegian national standardized tests between 2007 and 2019 (N = 936,708). These tests measure aptitude in math and reading comprehension, and are taken the years children turn 10, 13, and 14 y old. We identify millions of pairs of relatives within our sample (82 different kinds, in total), including not only conventional biological relatives such as siblings and cousins, but also relatives-in-law, relatives through adoption, twins, and relatives connected through twins. When fitting models which assume that family resemblance arises solely from additive genetic effects and assortative mating, we find that they describe much of our data well, but that they systematically underestimate the similarity of close relatives (particularly monozygotic twins), maternal relatives, relatives-in-law, and relatives through adoption. We discuss potential explanations for these deviations, including shared-environmental effects, nonadditive genetic effects, and gene–environment interplay.

• Torgalsbøen, Anne-Kari; Mohn, Christine; Larøi, Frank & Czajkowski, Nikolai Olavi (2025). Longitudinal recovery and self-efficacy in first-episode schizophrenia: insights from a 10-year follow-up study. Frontiers in Psychiatry. p. 01–09. doi: 10.3389/fpsyt2025.1588349. Full text in Research Archive Show summary

  Background: Research on clinical recovery rates in first-episode schizophrenia has yielded inconsistent results due to varying definitions of recovery and methodological differences. The longitudinal trajectory of recovery—whether rates improve, decline, or remain stable—remains unclear. Schizophrenia significantly impacts young lives, making it crucial to examine self-efficacy, the belief in one’s ability to manage adversity, and its relationship with clinical recovery. Methods: The Oslo Schizophrenia Recovery study`s repeated assessment design, including twelve clinical evaluations over ten years, is ideal for studying longitudinal recovery. Self-efficacy was measured using the General Perceived Self-Efficacy scale, with data analyzed through linear multilevel models. Twenty-eight well-defined first-episode schizophrenia patients were assessed yearly, using a strict recovery definition (two years of full symptom remission and adequate social/role functioning), with 79% of patients retained from baseline. Results: Recovery rates improved and remained stable, suggesting better outcomes than previously reported. Of the participants, 50% achieved clinical recovery. Recovered individuals showed a sharp increase in self-efficacy within the first year, while non-recovered patients exhibited gradual improvement. The interaction between recovery status and time revealed distinct self-efficacy trajectories, particularly in the first post-onset year. Conclusions: A significant proportion of first-episode schizophrenia patients can achieve clinical recovery. While these positive outcomes are noteworthy, it is important to recognize that recovery paths can vary widely among individuals. Since people with schizophrenia are concerned about their chances of recovery, the results must be shared with patients and their families. While the causal relationship between self-efficacy and recovery remains unclear, they likely influence each other.

• Hansen, Heidi Marie Umbach; Laeng, Bruno; Vassend, Olav Mandt; Czajkowski, Nikolai Olavi; Endestad, Tor & Danielsen, Anne [Show all 7 contributors for this article] (2025). The role of Big Five personality domains and facets in musical sensibility: a twin study. Scientific Reports. 15(1). doi: 10.1038/s41598-025-95661-z. Full text in Research Archive Show summary

  Musical sensibility can be understood as a propensity to be emotionally and aesthetically engaged by music and may constitute a key feature of a multidimensional definition of musicality. Yet, the nature of this construct is only just beginning to be understood. In a sample of adult Norwegian twins (N = 2592), we aimed to establish whether interindividual variability in musical sensibility may partially be attributable to personality, both in terms of the Big Five personality domains and their lower-order facets, as well as the role of genes and environments. Phenotypic analyses demonstrated that the personality domains of open-mindedness (and the facet aesthetic sensitivity in particular), agreeableness (and the facet compassion), and negative emotionality were all significantly associated with and predictive of musical sensibility. Multivariate biometric twin models further revealed that these relations were driven mainly by genetic influences, accounting for 50–100% of the observed covariance, whereas non-shared environmental influences accounted for the rest. Moreover, genetic correlations of musical sensibility with personality traits were substantial, and particularly strong for open-mindedness, pointing to considerable overlap in the biological mechanisms underlying the two traits. These findings situate musical sensibility within a broader network of psychological dispositions, possibly linked together via common affective systems.

• Torgalsbøen, Anne-Kari; Mohn, Hanne Christine; Larøi, Frank & Czajkowski, Nikolai Olavi (2025). Longitudinal recovery and self-efficacy in first-episode schizophrenia: insights from a 10-year follow-up study. Frontiers in Psychiatry. 16. doi: 10.3389/fpsyt.2025.1588349. Full text in Research Archive
• Skaug, Eirunn; Czajkowski, Nikolai Olavi; Waaktaar, Trine & Torgersen, Svenn Omar (2024). The Longitudinal Relationship Between Life Events and Loneliness in Adolescence: A Twin Study. Developmental Psychology. ISSN 0012-1649. 60(5), p. 966–977. doi: 10.1037/dev0001692. Full text in Research Archive Show summary

  The aim of the study was to examine associations between life events and self-assessed loneliness in adolescence. We used data from a Norwegian population-based twin sample including seven birth cohorts (N = 2,879, 56% females). The participants completed self-report questionnaires three times throughout adolescence, with 2 years in between (i.e., 12–18 years old at Wave 1). By using a random intercept cross-lagged panel model (RI-CLPM), we were able to separate stable influences in the measured constructs from the within-person changes at each measurement occasion. In addition, using data from twins allowed us to examine to what degree the associations between life events and loneliness were genetic and/or environmental in nature. The results showed moderate stability of both loneliness and aggregation scores of life events throughout adolescence. The life events were assigned to clusters based on their independence (i.e., events considered dependent or independent on a person’s behavior) and desirability (i.e., positive or negative). The time-stable between-person variance in all three measures, loneliness and person-dependent positive and negative life events, could almost exclusively be accounted for by genetic factors. However, as expected, also shared environmental factors influenced person-independent life events. The associations between time-stable between-person variance in loneliness and life events were small, and nearly exclusively due to shared genetic influences. Furthermore, life events do not seem to predict changes in loneliness or vice versa. In conclusion, the self-reported levels of loneliness throughout adolescence seems to be independent of life events.

• Mayerhofer, Lilian Juliane Kozlowski; Nes, Ragnhild Bang; Lan, Xiaoyu; Czajkowski, Nikolai Olavi; Ystrøm, Eivind & Røysamb, Espen (2024). Wellbeing and illbeing in women exposed to physical and sexual violence during peripregnancy: a population-based longitudinal study. European Journal of Psychotraumatology. 15(1). doi: 10.1080/20008066.2024.2398961. Full text in Research Archive Show summary

  Background: Physical and sexual violence against pregnant women have been associated with detrimental mental health outcomes for victims. Few studies have examined both positive (wellbeing) and negative (illbeing) mental health indicators in the same sample. Additionally, the literature assessing mental health based on different forms of violence is limited. Objective: To compare both wellbeing (life satisfaction) and illbeing (anxiety and depression) trajectories between non-victimized and victims of physical, sexual and both forms of violence that occurred during or shortly before pregnancy. Further, we analyse whether social support moderates these trajectories. Method: This longitudinal study is based on the Norwegian Mother, Father and Child Cohort, including the period from early pregnancy to toddlerhood (3 years). We compared wellbeing and illbeing trajectories of non-victims (n = 73,081), victims of physical abuse (n = 1076), sexual abuse (n = 683), and both forms of abuse (n = 107) using Growth Curve Modelling. Finally, social support was included as a moderator of wellbeing and illbeing trajectories. Results: Results indicated that victims scored systematically lower in wellbeing and higher in illbeing. Exposure to violence did not significantly change the wellbeing trajectory, pointing to similar developments in wellbeing among victims and non-victims for the considered period. On the other hand, different trajectories in illbeing occurred between victims and non-victims, as well as between victimized groups. Victims experienced greater change in illbeing scores, with a steeper decrease in illbeing compared to non-victims. Both victims and non-victims returned to respective baseline scores 3 years after birth. All women benefited from social support, but victims of physical abuse were particularly protected by social support. Conclusions: There is an alarming persistence of mental health problems in women exposed to violence during peripregnancy. Different forms of violence differentially impact women’s mental health. Social support is beneficial among all pregnant women.

• Fredriksen, Trude; Vatne, Torun Marie; Haukeland, Yngvild Bjartveit; Czajkowski, Nikolai Olavi; Wakefield, Claire E. & Fjermestad, Krister Westlye (2024). Evaluation of Siblings’ Perceived Relationship Outcomes with Their Parents in an Open Trial of the SIBS Intervention for Children with Chronic Disorders. Journal of Child and Family Studies. ISSN 1062-1024. 33. doi: 10.1007/s10826-024-02824-z. Full text in Research Archive Show summary

  The SIBS intervention aims to prevent mental health problems for siblings of children with chronic disorders and has shown promising results. The mechanisms behind these changes have not been examined. Parent-child relationship quality is a predictor of mental health in siblings. Our first objective was to investigate whether sibling-perceived relationship quality between siblings and parents changes over time after participating in SIBS. Second, as the intervention requires participation of only one parent, we examined with a dual scale (anxiety and avoidance attachment style) whether relationship quality was associated with which parent participated. Third, as SIBS aims to promote parents‘ communication skills, we examined whether sibling-perceived communication quality with parents predicted relationship quality over time. The sample comprised 99 siblings (M = 11.5 years, SD = 2.0; range 8–16; 54% girls, 46% boys) of children with chronic disorders and one parent per sibling (63% mothers). We administered the questionnaires at pre-intervention, at three- and 6-months postintervention. We applied growth curve models for relationship quality over time with communication quality as a predictor, controlling for parent gender. We found significant improvement in sibling-perceived relationship quality with the participating and the non-participating parent on the relationship anxiety scale over time, with small to medium effect sizes. Higher communication quality significantly predicted improvement of relationship quality in all four relationship outcomes. We conclude that change in relationship quality may be part of the positive outcomes of the SIBS intervention and is mainly explained by communication enhancement. Controlled trials of the SIBS intervention are indicated.

• Kleppestø, Thomas Haarklau; Czajkowski, Nikolai Olavi; Sheehy-Skeffington, Jennifer; Vassend, Olav; Røysamb, Espen & Eftedal, Nikolai Haahjem [Show all 9 contributors for this article] (2024). The genetic underpinnings of right-wing authoritarianism and social dominance orientation explain political attitudes beyond Big Five personality. Journal of Personality. ISSN 0022-3506. 92(6), p. 1744–1758. doi: 10.1111/jopy.12921. Full text in Research Archive Show summary

  Objective: Political attitudes are predicted by the key ideological variables of right-wing authoritarianism (RWA) and social dominance orientation (SDO), as well as some of the Big Five personality traits. Past research indicates that personality and ideological traits are correlated for genetic reasons. A question that has yet to be tested concerns whether the genetic variation underlying the ideological traits of RWA and SDO has distinct contributions to political attitudes, or if genetic variation in political attitudes is subsumed under the genetic variation underlying standard Big Five personality traits. Method: We use data from a sample of 1987 Norwegian twins to assess the genetic and environmental relationships between the Big Five personality traits, RWA, SDO, and their separate contributions to political policy attitudes. Results: RWA and SDO exhibit very high genetic correlation (r = 0.78) with each other and some genetic overlap with the personality traits of openness and agreeableness. Importantly, they share a larger genetic substrate with political attitudes (e.g., deporting an ethnic minority) than do Big Five personality traits, a relationship that persists even when controlling for the genetic foundations underlying personality traits. Conclusion: Our results suggest that the genetic foundations of ideological traits and political attitudes are largely non-overlapping with the genetic foundations of Big Five personality traits.

• Kleppestø, Thomas Haarklau; Czajkowski, Nikolai Olavi; Vassend, Olav Mandt; Røysamb, Espen; Eftedal, Nikolai Haahjem & Sheehy-Skeffington, Jennifer [Show all 10 contributors for this article] (2024). Attachment and Political Personality are Heritable and Distinct Systems, and Both Share Genetics with Interpersonal Trust and Altruism. Behavior Genetics. ISSN 0001-8244. 54, p. 321–332. doi: 10.1007/s10519-024-10185-y. Full text in Research Archive Show summary

  The attachment and caregiving domains maintain proximity and care-giving behavior between parents and offspring, in a way that has been argued to shape people’s mental models of how relationships work, resulting in secure, anxious or avoidant interpersonal styles in adulthood. Several theorists have suggested that the attachment system is closely connected to orientations and behaviors in social and political domains, which should be grounded in the same set of familial experiences as are the different attachment styles. We use a sample of Norwegian twins (N = 1987) to assess the genetic and environmental relationship between attachment, trust, altruism, right-wing authoritarianism (RWA), and social dominance orientation (SDO). Results indicate no shared environmental overlap between attachment and ideology, nor even between the attachment styles or between the ideological traits, challenging conventional wisdom in developmental, social, and political psychology. Rather, evidence supports two functionally distinct systems, one for navigating intimate relationships (attachment) and one for navigating social hierarchies (RWA/SDO), with genetic overlap between traits within each system, and two distinct genetic linkages to trust and altruism. This is counter-posed to theoretical perspectives that link attachment, ideology, and interpersonal orientations through early relational experiences.

• Hansen, Heidi Marie Umbach; Røysamb, Espen; Vassend, Olav Mandt; Czajkowski, Nikolai Olavi; Endestad, Tor & Danielsen, Anne [Show all 7 contributors for this article] (2024). The underlying architecture of musical sensibility: One general factor, four subdimensions, and strong genetic effects. Annals of the New York Academy of Sciences. ISSN 0077-8923. 1540(1), p. 291–306. doi: 10.1111/nyas.15227. Full text in Research Archive Show summary

  Current evidence suggests moderate heritability of music phenotypes, such as music listening and achievement. However, other fundamental traits underlying people's interest in music and its relevance for their lives have been largely neglected, and little is known about the genetic and environmental etiology of what we refer to as musical sensibility—the tendency to be emotionally and aesthetically engaged by music. This study investigated the latent structure, as well as the genetic and environmental factors influencing individual variability in multiple domains of musical sensibility, and the etiological architecture of the relationship between the dimensions. To this end, we used phenotypic confirmatory factor analytic and biometric twin modeling to analyze self-reported ratings on four dimensions of musical sensibility in a sample of Norwegian twins (N = 2600). The results indicate a phenotypic higher-order structure, whereby both the resulting general musical sensibility factor and the conceptually narrower domains were strongly heritable (49–65%). Multivariate analyses of the genetic and environmental covariance further revealed substantial overlap in genetic variance across domains.

• Fardzadeh, Haghish Ebad; Czajkowski, Nikolai Olavi; Walby, Fredrik Andreas; Qin, Ping & Laeng, Bruno (2024). Suicide attempt risk predicts inconsistent self-reported suicide attempts: A machine learning approach using longitudinal data. Journal of Affective Disorders. ISSN 0165-0327. 355, p. 495–504. doi: 10.1016/j.jad.2024.03.133. Full text in Research Archive Show summary

  Introduction Inconsistent self-reports of lifetime suicide attempts (LSAs) are a major obstacle for accurate assessment of suicidal behavior. This study is the first to posit that adolescents at higher risk report LSAs more consistently than those at lower risk, revealing a link between suicide attempt risk and consistent reporting. Methods A machine learning model was trained with 70 % of the baseline assessment data of a longitudinal sample of Norwegian adolescents (n = 10,739). The model was used to estimate the LSA risk score for the remaining 30 % of the testing dataset. The relationship between these baseline risk scores and the consistency of reporting LSAs was assessed using a 2-year follow-up reassessment of the testing dataset. Results Internalizing problems, optimism about the future, conduct problems, substance use, and disordered eating were important factors associated with suicide attempt risk. Of the participants, 63.41 % had inconsistent self-reports at the two-year follow-up. Adolescents who consistently reported LSAs had significantly higher scores of suicide attempt risk at baseline. Two logistic regression analyses confirmed an association between suicide attempt risk and inconsistent self-reported LSAs and showed that sex (being male), and lower levels of depression and conduct problems significantly predicted such inconsistencies. Those who inconsistently reported LSAs were more likely than the others to be classified by the model as false negatives at the baseline risk assessment due to their lower estimated risk scores. Limitations Suicide attempts were measured with a single item in this study. Conclusion These risk factors support the theory of adolescent suicidality (TAS) and could improve suicide attempt risk assessment. Inconsistent self-reported LSAs signal lower suicide attempt risk.

• Bjørndal, Ludvig Daae; Ebrahimi, Omid V.; Røysamb, Espen; Karstoft, Karen-Inge; Czajkowski, Nikolai Olavi & Nes, Ragnhild Bang (2024). Stressful life events exhibit complex patterns of associations with depressive symptoms in two population-based samples using network analysis. Journal of Affective Disorders. ISSN 0165-0327. 349, p. 569–576. doi: 10.1016/j.jad.2024.01.054. Full text in Research Archive Show summary

  Background Stressful life events (SLEs) constitute key risk factors for depression. However, previous studies examining associations between SLEs and depression have been limited by focusing on single events, combining events into broad categories, and/or ignoring interrelationships between events in statistical analyses. Network analysis comprises a set of statistical methods well-suited for assessing relationships between multiple variables and can help surpass several limitations of previous studies. Methods We applied network analysis using mixed graphical models combining two large-scale population-based samples and >34,600 randomly sampled adults to investigate the associations between SLEs and current depressive symptoms in the general population. Results Numerous SLEs were uniquely associated with specific symptoms. Strong pairwise links were observed between SLEs during the past year and individual symptoms, e.g., between having experienced illness or injury and sleeping problems, having been degraded or humiliated and feeling blue, and between financial problems and hopelessness and being worried and anxious. Several SLEs, such as financial problems, sexual abuse, and having been degraded or humiliated, were associated with symptoms across more than one timepoint. More recent SLEs were generally more strongly associated with depressive symptoms. Several life events were strongly interrelated, such as multiple forms of abuse, and financial problems, unemployment, divorce, and serious illness or injury. Limitations Limitations include a retrospective SLE measure, cross-sectional data, a brief self-report measure of depressive symptoms, and possible attrition bias in the sample. Conclusions Our findings may have implications for public health efforts seeking to improve population mental health.

• Prydz, Monica Beer; Czajkowski, Nikolai Olavi; Eilertsen, Maja; Røysamb, Espen & Nes, Ragnhild Bang (2024). A Web-Based Intervention Using "Five Ways to Wellbeing" to Promote Well-Being and Mental Health: Randomized Controlled Trial. JMIR Mental health. 11. doi: 10.2196/49050. Full text in Research Archive Show summary

  Background: Compromised well-being and mental health problems pose a significant threat to individuals and societies worldwide. Resource-intensive psychological treatments alone cannot alleviate this burden. There is a need for low-cost, evidence-based interventions aimed at preventing illness and promoting well-being. Five activity domains appear to be linked with well-being promotion across populations: connecting with others, being active, taking notice, learning, and being generous/giving. The activities mentioned are part of the Five Ways to Wellbeing framework and the web-based intervention Five Ways to Wellbeing for All (5waysA). Objective: This randomized controlled trial aims to test the effects of the 5waysA intervention, a web-based, low-cost, well-being–promoting measure targeting the general population. To date, the Five Ways to Wellbeing framework has not been tested in this specific format. The 5waysA intervention comprises 2 webinars and SMS text message reminders delivered over a 10-week period. Methods: In 2021, a total of 969 study participants from various regions across Norway were openly recruited through a web page. They were then randomly assigned to either an intervention group or 1 of 2 waiting list control groups, namely, active or passive. Self-reported life satisfaction (Satisfaction With Life Scale [SWLS]), flourishing (Flourishing Scale [FS]), positive emotions, anxiety, and depression symptoms (Hopkins Symptom Checklist-8 [HSCL-8]) were assessed before the intervention, at 4 weeks into the intervention, and 1-2 weeks after the intervention (over 10 weeks). Data analysis was conducted using linear mixed (multilevel) models. Results: After 10 weeks, 453 participants (171 in the intervention group and 282 in the waiting list control group) were assessed on outcome variables, with a dropout rate of 53.2% (516/969). Results revealed a significantly greater increase in the intervention group compared with the controls for SWLS (b=0.13, 95% CI 0.03-0.23; P=.001), FS (b=0.19, 95% CI 0.08-0.30; P=.001), positive emotions (b=0.43, 95% CI 0.27-0.60; P<.001), and these factors combined into a global well-being measure (b=0.28, CI 0.16-0.39; P<.001). Effect sizes (Cohen d) for the well-being outcomes ranged from 0.30 to 0.49. In addition, a significant decrease in anxiety and depressive symptoms was observed (b=–0.17, 95% CI –0.30 to –0.04; P=.001) with an effect size (Cohen d) of –0.20. Conclusions: The findings suggest that the web-based 5waysA intervention could serve as an effective approach for enhancing well-being and mental health within the general population. This study offers individuals, policy makers, and local stakeholders an accessible and potentially cost-effective well-being intervention that could be easily implemented.

• Bjørndal, Ludvig Daae; Nes, Ragnhild Bang; Czajkowski, Nikolai Olavi & Røysamb, Espen (2023). The structure of well-being: a single underlying factor with genetic and environmental influences. Quality of Life Research. ISSN 0962-9343. 32, p. 2805–2816. doi: 10.1007/s11136-023-03437-7. Full text in Research Archive
• Fardzadeh, Haghish Ebad; Nes, Ragnhild Bang; Obaidi, Milan; Qin, Ping; Stänicke, Line Indrevoll & Bekkhus, Mona [Show all 8 contributors for this article] (2023). Unveiling Adolescent Suicidality: Holistic Analysis of Protective and Risk Factors Using Multiple Machine Learning Algorithms. Journal of Youth and Adolescence. ISSN 0047-2891. 53, p. 507–525. doi: 10.1007/s10964-023-01892-6. Full text in Research Archive Show summary

  Abstract Adolescent suicide attempts are on the rise, presenting a significant public health concern. Recent research aimed at improving risk assessment for adolescent suicide attempts has turned to machine learning. But no studies to date have examined the performance of stacked ensemble algorithms, which are more suitable for low-prevalence conditions. The existing machine learning-based research also lacks population-representative samples, overlooks protective factors and their interplay with risk factors, and neglects established theories on suicidal behavior in favor of purely algorithmic risk estimation. The present study overcomes these shortcomings by comparing the performance of a stacked ensemble algorithm with a diverse set of algorithms, performing a holistic item analysis to identify both risk and protective factors on a comprehensive data, and addressing the compatibility of these factors with two competing theories of suicide, namely, The Interpersonal Theory of Suicide and The Strain Theory of Suicide. A population-representative dataset of 173,664 Norwegian adolescents aged 13 to 18 years (mean = 15.14, SD = 1.58, 50.5% female) with a 4.65% rate of reported suicide attempt during the past 12 months was analyzed. Five machine learning algorithms were trained for suicide attempt risk assessment. The stacked ensemble model significantly outperformed other algorithms, achieving equal sensitivity and a specificity of 90.1%, AUC of 96.4%, and AUCPR of 67.5%. All algorithms found recent self-harm to be the most important indicator of adolescent suicide attempt. Exploratory factor analysis suggested five additional risk domains, which we labeled internalizing problems, sleep disturbance, disordered eating, lack of optimism regarding future education and career, and victimization. The identified factors provided stronger support for The Interpersonal Theory of Suicide than for The Strain Theory of Suicide. An enhancement to The Interpersonal Theory based on the risk and protective factors identified by holistic item analysis is presented.

• Fardzadeh, Haghish Ebad; Czajkowski, Nikolai Olavi & Soest, Tilmann Martin von (2023). Predicting suicide attempts among Norwegian adolescents without using suicide-related items: a machine learning approach. Frontiers in Psychiatry. 14. doi: 10.3389/fpsyt.2023.1216791. Full text in Research Archive Show summary

  Introduction: Research on the classification models of suicide attempts has predominantly depended on the collection of sensitive data related to suicide. Gathering this type of information at the population level can be challenging, especially when it pertains to adolescents. We addressed two main objectives: (1) the feasibility of classifying adolescents at high risk of attempting suicide without relying on specific suicide-related survey items such as history of suicide attempts, suicide plan, or suicide ideation, and (2) identifying the most important predictors of suicide attempts among adolescents. Methods: Nationwide survey data from 173,664 Norwegian adolescents (ages 13–18) were utilized to train a binary classification model, using 169 questionnaire items. The Extreme Gradient Boosting (XGBoost) algorithm was fine-tuned to classify adolescent suicide attempts, and the most important predictors were identified. Results: XGBoost achieved a sensitivity of 77% with a specificity of 90%, and an AUC of 92.1% and an AUPRC of 47.1%. A coherent set of predictors in the domains of internalizing problems, substance use, interpersonal relationships, and victimization were pinpointed as the most important items related to recent suicide attempts. Conclusion: This study underscores the potential of machine learning for screening adolescent suicide attempts on a population scale without requiring sensitive suicide-related survey items. Future research investigating the etiology of suicidal behavior may direct particular attention to internalizing problems, interpersonal relationships, victimization, and substance use.

• Mayerhofer, Lilian Juliane Kozlowski; Nes, Ragnhild Bang; Lan, Xiaoyu; Czajkowski, Nikolai Olavi; Ystrøm, Eivind & Røysamb, Espen (2023). Wellbeing and illbeing in women exposed to physical and sexual violence: A population based longitudinal study. OSF Preprints. Full text in Research Archive
• Fardzadeh, Haghish Ebad & Czajkowski, Nikolai Olavi (2023). Reconsidering False Positives in Machine Learning Binary Classification Models of Suicidal Behavior. Current Psychology. ISSN 1046-1310. doi: 10.1007/s12144-023-05174-z. Full text in Research Archive Show summary

  Abstract We posit the hypothesis that False Positive cases (FP) in machine learning classification models of suicidal behavior are at risk of suicidal behavior and should not be seen as sheer classification error. We trained an XGBoost classification model using survey data from 173,663 Norwegian adolescents and compared the classification groups for several suicide-related mental health indicators, such as depression, anxiety, psychological distress, and non-suicidal self-harm. The results showed that as the classification is made at higher risk thresholds - corresponding to higher specificity levels - the severity of anxiety and depression symptoms of the FP and True Positive cases (TP) become significantly more similar. In addition, psychological distress and non-suicidal self-harm were found to be highly prevalent among the FP group, indicating that they are indeed at risk. These findings demonstrate that FP are a relevant risk group for potential suicide prevention programs and should not be dismissed. Although our findings support the hypothesis, we account for limitations that should be examined in future longitudinal studies. Furthermore, we elaborate on the rationale of the hypothesis, potential implications, and its applicability to other mental health outcomes.

• Fardzadeh, Haghish Ebad; Laeng, Bruno & Czajkowski, Nikolai Olavi (2023). Are false positives in suicide classification models a risk group? Evidence for “true alarms” in a population-representative longitudinal study of Norwegian adolescents. Frontiers in Psychology. 14. doi: 10.3389/fpsyg.2023.1216483. Full text in Research Archive Show summary

  Introduction False positives in retrospective binary suicide attempt classification models are commonly attributed to sheer classification error. However, when machine learning suicide attempt classification models are trained with a multitude of psycho-socio-environmental factors and achieve high accuracy in suicide risk assessment, false positives may turn out to be at high risk of developing suicidal behavior or attempting suicide in the future. Thus, they may be better viewed as “true alarms,” relevant for a suicide prevention program. In this study, using large population-based longitudinal dataset, we examine three hypotheses: (1) false positives, compared to the true negatives, are at higher risk of suicide attempt in future, (2) the suicide attempts risk for the false positives increase as a function of increase in specificity threshold; and (3) as specificity increases, the severity of risk factors between false positives and true positives becomes more similar. Methods Utilizing the Gradient Boosting algorithm, we used a sample of 11,369 Norwegian adolescents, assessed at two timepoints (1992 and 1994), to classify suicide attempters at the first time point. We then assessed the relative risk of suicide attempt at the second time point for false positives in comparison to true negatives, and in relation to the level of specificity. Results We found that false positives were at significantly higher risk of attempting suicide compared to true negatives. When selecting a higher classification risk threshold by gradually increasing the specificity cutoff from 60% to 97.5%, the relative suicide attempt risk of the false positive group increased, ranging from minimum of 2.96 to 7.22 times. As the risk threshold increased, the severity of various mental health indicators became significantly more comparable between false positives and true positives. Conclusion We argue that the performance evaluation of machine learning suicide classification models should take the clinical relevance into account, rather than focusing solely on classification error metrics. As shown here, the so-called false positives represent a truly at-risk group that should be included in suicide prevention programs. Hence, these findings should be taken into consideration when interpreting machine learning suicide classification models as well as planning future suicide prevention interventions for adolescents.

• Torgalsbøen, Anne Kari; Mohn, Christine; Larøi, Frank; Fu, Susie & Czajkowski, Nikolai Olavi (2023). A ten-year longitudinal repeated assessment study of cognitive improvement in patients with first-episode schizophrenia and healthy controls: The Oslo Schizophrenia Recovery (OSR) study. Schizophrenia Research. ISSN 0920-9964. 260, p. 92–98. doi: 10.1016/j.schres.2023.08.008. Full text in Research Archive Show summary

  The mapping of cognitive trajectories after a first episode of schizophrenia has been the aim in several studies, but the longitudinal course of cognitive impairments remains an important question. Due to methodological limitations, it has been challenging to pinpoint specific periods of improvement or stability in cognitive functioning over time. The objective of this study is to further clarify the longitudinal course of cognitive change after a first episode of schizophrenia through frequent repeated measurement. A total of 56 persons participated in the study (28 first episode patients and 28 healthy pairwise matched controls) with 79 % of patients retained at the 10-year follow-up. The Oslo Schizophrenia Recovery study has a repeated measurement design and includes data from nine cognitive assessments over 10 years. Cognition was assessed with the MATRICS Consensus Cognitive Battery, which is well suited for repeated measurements. Data were analyzed with linear multilevel models. The results challenge some of the views about the course of cognitive impairment in first-episode schizophrenia patients. Using quadratic time effects in our analyses and balancing the patient group with regards to the most relevant confounding demographic variables such as age, gender, and education, we showed that cognitive deficits change and improve more than in healthy individuals until year 6, when both groups stabilize. The patient group improved on some of the most important cognitive domains associated with functional outcome with 63.5 % full recovery at 10-year follow-up.

• Tsotsi, Stella; Goh, Shaun; Coplan, Robert J.; Bølstad, Evalill; Czajkowski, Nikolai Olavi & Smajlagic, Dinka [Show all 7 contributors for this article] (2023). Co-occurrence of internalizing difficulties and aggression in early childhood and risk of mental health problems in middle childhood. International Journal of Behavioral Development. ISSN 0165-0254. 47(5), p. 384–396. doi: 10.1177/01650254231187902. Full text in Research Archive Show summary

  The goal of this prospective longitudinal study was to explore whether co-occurrent internalizing difficulties and aggression in early childhood convey increased risk for later mental health problems in middle childhood. Participants were mothers from the Norwegian Mother, Father and Child Cohort Study (MoBa), who provided assessments of child internalizing difficulties and aggression at ages 3 years ( n = 54,644; 26,750 girls) and 5 years ( n = 38,177; 18,794 girls), as measures of child depressive, anxiety, conduct-related, and oppositional defiant (OD) symptoms at age 8 years. Using latent profile analyses (LPA) of internalizing difficulties and aggression, four profiles were identified: low-symptom/normative; primarily internalizing; primarily aggressive; and co-occurrent. Among the other results, the co-occurrent group exhibited the highest levels of depressive, anxiety, and oppositional defiant symptoms at 8 years. Most children (78%) remained stable in their profile between ages 3 and 5 years. Among the transition patterns that emerged, transitions were observed both from the normative to a risk profile and vice versa. Children who remained stable within the co-occurrent profile or who transitioned from the co-occurrent profile to one of the other two risk profiles also exhibited more depressive, anxiety, and OD symptoms at 8 years of age, when compared with children who transitioned from the co-occurrent to the normative profile. The heterogeneity between early manifestation of internalizing difficulties and aggression, and specific type of later mental health symptoms not only supports a shared etiology between internalizing and externalizing difficulties but also points toward the need for person-centered monitoring in early childhood with further implications for early identification of difficulties and preventive measures.

• Tesli, Martin Steen; Nesvåg, Ragnar; Haukvik, Unn Kristin Hansen; Gustavson, Kristin; Tesli, Natalia & Friestad, Christine [Show all 12 contributors for this article] (2023). Common genetic and environmental risk for personality disorders and psychotic-like experiences in young adult twins. Acta Psychiatrica Scandinavica. ISSN 0001-690X. 148(6), p. 561–569. doi: 10.1111/acps.13596. Full text in Research Archive Show summary

  Abstract Introduction Psychotic‐like experiences (PLE) have been associated with the subsequent emergence of psychotic disorders as well as several other domains of psychopathology. In this twin study, we estimated the genetic and environmental correlations between PLE and 10 personality disorders (PD). Methods Diagnoses of 10 PDs according to the Diagnostic and Statistical Manual of Mental Disorders (DSM‐IV) and PLE from the Composite International Diagnostic Interview (CIDI) were retrieved for 2793 young adult twins from the Norwegian Twin Registry. Risk for having a PD and PLEs was modeled using item response theory. Biometric twin models were fitted to estimate the genetic and environmental correlations between PDs and PLEs. Co‐twin control analysis was performed to estimate additional within‐family risk for PLEs when having a PD. Results Phenotypic overlap between PDs and PLEs ranged from 14% to 44% in males and from 11% to 39% in females, with the highest overlap for borderline PD in both sexes. In general, we found higher genetic correlations ( r  = 0.14–0.72) than environmental correlations ( r  = 0.06–0.28) between PDs and PLEs. The highest genetic correlations between PLE and PDs were found for borderline ( r  = 0.72), paranoid ( r  = 0.56), schizotypal ( r  = 0.56) and antisocial PD (r = 0.49). Conclusion We found that the co‐occurrence between PDs and PLE is the best explained by shared genetic determinants, with minor contributions from environmental factors. Interestingly, borderline PD was highly genetically correlated with PLE, warranting molecular genetic studies of this association.

• Rosenström, Tom H.; Czajkowski, Nikolai Olavi; Solbakken, Ole Andre & Saarni, Suoma E. (2023). Direction of dependence analysis for pre-post assessments using non-Gaussian methods: a tutorial. Psychotherapy Research. ISSN 1050-3307. doi: 10.1080/10503307.2023.2167526. Full text in Research Archive
• Oftedal, Aurora; Bekkhus, Mona; Haugen, Guttorm Nils; Czajkowski, Nikolai Olavi & Kaasen, Anne (2022). The impact of diagnosed fetal anomaly, diagnostic severity and prognostic ambiguity on parental depression and traumatic stress: a prospective longitudinal cohort study. Acta Obstetricia et Gynecologica Scandinavica. ISSN 0001-6349. 101(11), p. 1291–1299. doi: 10.1111/aogs.14453. Full text in Research Archive Show summary

  Introduction - The detection of a fetal anomaly during routine obstetric ultrasound is a potentially traumatic experience. The aim of this study is to examine longitudinally the impact of diagnosis of fetal anomaly on symptoms of depression and traumatic stress among mothers and fathers, and to examine how variations in psychological adjustment relate to diagnostic severity and prognostic ambiguity.<p> <p>Material and methods - In this prospective observational study conducted at a tertiary perinatal referral center, 81 mothers and 69 fathers with ultrasound findings of fetal anomaly completed the Edinburgh Postnatal Depression Scale (EPDS) and Impact of Events Scale (IES) at four time points in pregnancy (T1–T4) and 6 weeks after birth (T5). We compared this with depression and traumatic stress in a sample of non-affected parents (n = 110 mothers, 98 fathers).<p> <p>Results - Linear mixed effects models indicated that parents who received a diagnosis of fetal anomaly experienced higher levels of depression and traumatic stress over time, compared with non-affected parents. Depression: mean difference mothers = 4.46 ± 0.47, fathers = 2.80 ± 0.42. Traumatic stress: mean difference mothers = 20.04 ± 2.13, fathers = 12.66 ± 1.74. Parents with a more severe diagnosis experienced elevated symptoms compared with parents with a less severe diagnosis. Among mothers, prognostic ambiguity and changes in the anticipated diagnosis after birth were also associated with increased distress, regardless of whether the change was for the better or worse.<p> <p>Conclusions - Diagnosis of fetal anomaly increases risk of depression and traumatic stress in expectant mothers and fathers, both acutely and over time.

• Eftedal, Nikolai Haahjem; Kleppestø, Thomas Haarklau; Czajkowski, Nikolai Olavi; Sheehy-Skeffington, Jennifer; Røysamb, Espen & Vassend, Olav Mandt [Show all 8 contributors for this article] (2022). Justice sensitivity is undergirded by separate heritable motivations to be morally principled and opportunistic. Scientific Reports. 12. doi: 10.1038/s41598-022-09253-2. Full text in Research Archive Show summary

  Abstract Injustice typically involves some people benefitting at the expense of others. An opportunist might then be selectively motivated to amend only the injustice that is harmful to them, while someone more principled would respond consistently regardless of whether they stand to gain or lose. Here, we disentangle such principled and opportunistic motives towards injustice. With a sample of 312 monozygotic- and 298 dizygotic twin pairs (N = 1220), we measured people’s propensity to perceive injustice as victims, observers, beneficiaries, and perpetrators of injustice, using the Justice Sensitivity scale. With a biometric approach to factor analysis, that provides increased stringency in inferring latent psychological traits, we find evidence for two substantially heritable factors explaining correlations between Justice Sensitivity facets. We interpret these factors as principled justice sensitivity (h 2  = 0.45) leading to increased sensitivity to injustices of all categories, and opportunistic justice sensitivity (h 2  = 0.69) associated with increased sensitivity to being a victim and a decreased propensity to see oneself as a perpetrator. These novel latent constructs share genetic substrate with psychological characteristics that sustain broad coordination strategies that capture the dynamic tension between honest cooperation versus dominance and defection, namely altruism, interpersonal trust, agreeableness, Social Dominance Orientation and opposition to immigration and foreign aid.

• Skaug, Eirunn; Czajkowski, Nikolai Olavi; Waaktaar, Trine & Torgersen, Svenn (2022). The role of sense of coherence and loneliness in borderline personality disorder traits: a longitudinal twin study. Borderline Personality Disorder and Emotion Dysregulation. 9. doi: 10.1186/s40479-022-00190-0. Full text in Research Archive Show summary

  Background Borderline personality disorder (BPD) implies having problems with identity and relations with other people. However, not much is known about whether these indications of BPD are present in adolescence, i.e., before personality disorders usually are diagnosed. In this study, we examined the prediction of an aspect of identity (i.e., sense of coherence [SOC]) and social relations (i.e., perceived loneliness) throughout adolescence on BPD traits in young adulthood. In addition, we examined to what degree the predictive ability could be attributed to genetic and environmental factors. We also examined whether life events in adolescence were related to BPD traits. Methods Three thousand three hundred ninety-one twins, consisting of seven national birth cohorts from Norway, participated in the study. SOC, loneliness and life events were measured three times throughout adolescence with self-report questionnaires, with 2 years in between measurements. BPD traits were measured at the end of adolescence around the age of 19 with a structured interview. Regression analyses were performed to examine the prediction of SOC, loneliness and life events on BPD traits. Cholesky decomposition models were then used to determine to what degree the associations were due to genetic and environmental influences. Results The prediction of SOC and loneliness on BPD traits increased from R = .25 (when measured 6 years prior to the assessment of BPD traits) to R = .45 (when measured shortly before the assessment of BPD traits). In addition, negative life events considered dependent on a person’s behavior were related to BPD traits. Negative independent and positive dependent life events did not contribute to the prediction of BPD traits. Cholesky decomposition models showed that SOC and loneliness were associated with BPD traits mainly due to shared genetic influences (i.e., the proportion due to genetic influences ranged from 71 to 86%). Adding negative dependent life events to the prediction of BPD traits did not change these percentages. Conclusions These findings indicate that the weaker SOC, the stronger feelings of loneliness, and the negative life events associated with BPD traits are mainly consequences of the genetic aspects of BPD traits, rather than having direct effects on levels of BPD symptoms.

• Skaug, Eirunn; Czajkowski, Nikolai Olavi; Waaktaar, Trine & Torgersen, Svenn (2022). Childhood Trauma and Borderline Personality Disorder Traits: A Discordant Twin Study. Journal of Psychopathology and Clinical Science. ISSN 2769-7541. 131(4), p. 365–374. doi: 10.1037/abn0000755. Full text in Research Archive
• Skaug, Eirunn; Czajkowski, Nikolai Olavi; Waaktaar, Trine & Torgersen, Svenn (2022). The relationship between life events and sense of coherence in adolescence. A longitudinal twin study. Journal of Research in Personality. ISSN 0092-6566. 99. doi: 10.1016/j.jrp.2022.104259. Full text in Research Archive Show summary

  This three-wave study examined the relationship between life events and sense of coherence (SOC) throughout adolescence by using genetically informative random intercept cross-lagged panel models. We also examined the genetic and environmental contribution to variance in the measured constructs. The data come from a Norwegian population-based twin sample (N = 2,878). Life events and SOC were associated, and both showed substantial genetic variance. Negative longitudinal effects were observed from negative dependent life events to SOC, from SOC to negative dependent life events and from SOC to positive dependent life events. However, these longitudinal effects were negligible in magnitude. In summary, the associations between all three clusters of life events and SOC were almost completely accounted for by shared genetic influences.

• Vassend, Olav Mandt; Czajkowski, Nikolai Olavi; Røysamb, Espen & Nielsen, Christopher Sivert (2022). The role of neuroticism and pain in dental anxiety: A twin study. Community Dentistry and Oral Epidemiology. ISSN 0301-5661. doi: 10.1111/cdoe.12763. Full text in Research Archive Show summary

  Objectives Accumulating evidence has revealed that dental anxiety is robustly associated with dental care-related pain and discomfort, but also with the personality trait of neuroticism (i.e. the relatively stable disposition to experience the world as distressing, threatening and unsafe). However, there is a near absence of research on these risk factors in samples for which genetic information is available. With the aim of arriving at a more refined understanding of dental anxiety, this twin cohort study assessed genetic and environmental influences on neuroticism, dental care-related pain and dental anxiety, and the relation between these phenotypes. Methods Participants were recruited from the Norwegian Twin Registry, and data collections were carried out in 1992–98 (Time 1) and 2011 (Time 2). Well-validated questionnaires were used to assess the study variables, including Corah's Dental Anxiety Scale, the Numerical Pain Rating Scale, the NEO Personality Inventory Revised (Time 2) and Eysenck's Personality Questionnaire (Time 1). Pearson correlation analysis and generalized estimating equations (GEE) were used to investigate phenotypic associations. Analyses of genetic and environmental influences were performed using Cholesky modelling. Results A total of 746 monozygotic (MZ) and 770 dizygotic (DZ) twins in the age group of 50–65 participated in the study. Moderate estimates of heritability for dental anxiety (0.29), treatment-related pain (0.24) and neuroticism (0.45–0.54) were found. Cholesky modelling showed furthermore that neuroticism assessed at Time 1 and Time 2 was related to dental anxiety and pain via both genetic and individual-specific environmental pathways, albeit not very strongly. The particularly high phenotypic correlation observed between dental care-related pain and anxiety (r = .68) was explained by both overlapping genetic and individual-specific environmental influences (the genetic and environmental correlations were .84 and .63 respectively). Conclusions The findings provide deeper insight into the aetiology of dental anxiety and confirm that while it is strongly linked to treatment-related pain experiences, this relation is to a considerable degree independent of general negative affectivity/neuroticism.

• Oftedal, Aurora; Bekkhus, Mona; Haugen, Guttorm Nils; Hjemdal, Odin; Czajkowski, Nikolai Olavi & Kaasen, Anne (2022). Long-Term Impact of Diagnosed Fetal Anomaly on Parental Traumatic Stress, Resilience, and Relationship Satisfaction. Journal of Pediatric Psychology. ISSN 0146-8693. 48(2), p. 181–192. doi: 10.1093/jpepsy/jsac085. Full text in Research Archive Show summary

  Knowledge regarding the long-term psychological adjustment of parents to children with prenatal diagnosis of congenital malformation is scarce. The aim of this study is to examine traumatic stress trajectories, resilience, and relationship satisfaction among parents to children with prenatal diagnosis of a congenital malformation, and to compare this to a sample of non-affected parents. Methods A prospective longitudinal cohort study was conducted at a tertiary perinatal referral center. Ninety-three mothers and 80 fathers who received a diagnosis of fetal anomaly during obstetric ultrasound examination (study group), and 110 mothers and 98 fathers with normal ultrasound findings (comparison group), reported their traumatic stress at four timepoints during pregnancy (T1-T4), 6 weeks after birth (T5), and 10-12 years after birth (T6). Resilience and relationship satisfaction was reported at 10-12 years after birth. Results Parents to children with a congenital malformation experienced significantly elevated traumatic stress levels over time, compared with parents of children without congenital malformation. The difference between groups was largest acutely after diagnosis and remained significant 10-12 years after the birth of the child. Resilience and relationship satisfaction levels were similar in both groups. Conclusions Despite experiencing high levels of traumatic stress over time, parents to children with a congenital malformation reported resilience and relationship satisfaction at similar levels to non-affected parents. This suggests that despite ongoing long-term distress, parents are still able to maintain positive psychological coping resources.

• Waraan, Luxsiya; Siqveland, Johan; Hanssen-Bauer, Ketil; Czajkowski, Nikolai Olavi; Axelsdottir, Brynhildur & Mehlum, Lars [Show all 7 contributors for this article] (2022). Family therapy for adolescents with depression and suicidal ideation: A systematic review and meta–analysis. Clinical Child Psychology and Psychiatry. ISSN 1359-1045. p. 1–19. doi: 10.1177/13591045221125005. Full text in Research Archive Show summary

  Objective To systematically review and meta-analyze the effectiveness of family therapy compared to other active treatments for adolescents with depressive disorders or suicidal ideation. Method We conducted a systematic search of The Cochrane Central Register of Controlled Trials, Medline, Embase, PsycINFO, AMED, CINAHL and Web of Science and performed two meta-analyses of outcomes for depressive symptoms and suicidal ideation. Results We screened 5,940 records and identified 10 randomized controlled studies of family therapy for depressive disorder or suicidal ideation in adolescents with an active treatment comparison group. Nine studies reported outcome measures of depressive symptoms and four reported outcome measures of suicidal ideation. The meta-analysis showed no significant difference between family therapy and active comparison treatments for end-of-treatment levels of depression. For suicidal ideation our meta-analysis showed a significant effect in favour of family therapy over comparison treatments for suicidal ideation. Conclusions Based on the current body of research, we found that family therapy is not superior to other psychotherapies in the treatment of depressive disorder. However, family therapy leads to significantly improved outcomes for suicidal ideation, compared to other psychotherapies. The evidence for the treatment of depression is of low quality needs more research.

• Kendler, Kenneth S.; Czajkowski, Nikolai Olavi & Reichborn-Kjennerud, Ted (2022). Ludvig Dahl's psychiatric genetic studies in his 1859 monograph: “Contribution to the knowledge of insanity in Norway”. American Journal of Medical Genetics Part B: Neuropsychiatric Genetics. ISSN 1552-4841. 189(6), p. 177–184. doi: 10.1002/ajmg.b.32914. Full text in Research Archive
• Mylläri, Sanna; Saarni, Suoma Eeva; Ritola, Ville; Joffe, Grigori; Stenberg, Jan-Henry & Solbakken, Ole Andre [Show all 8 contributors for this article] (2022). Text Topics and Treatment Response in Internet-Delivered Cognitive Behavioral Therapy for Generalized Anxiety Disorder: Text Mining Study. Journal of Medical Internet Research (JMIR). ISSN 1439-4456. 24(11). doi: 10.2196/38911. Full text in Research Archive
• Sælid, Gry Anette; Czajkowski, Nikolai Olavi; Aarø, Leif Edvard; Andersen, John Roger; Idsøe, Thormod & Helleseter, Miguel Delgado [Show all 7 contributors for this article] (2022). Effects of a school-based intervention on levels of anxiety and depression: a cluster-randomized controlled trial of the MindPower program in ten high schools in Norway. BMC Psychology. 10(14), p. 1–14. doi: 10.1186/s40359-022-00721-y. Full text in Research Archive Show summary

  Background The previous decades have shown increased symptoms of depression and anxiety among adolescents. To promote mental health and reduce mental illness, the government of Norway has, as in other countries, pledged that all schools must incorporate life-skills education. We report results from an evaluation of MindPower, a modification of the Coping With Depression (CWD) course, delivered universally in the classroom to secondary high school students, aged 15–16 years, in one county in Norway. The aim of the study was to evaluate the effect of MindPower on symptoms of depression and anxiety. Methods We utilized a two-groups` delayed intervention design where 110 first year high school classes were randomized into one of two intervention groups (IG1 and IG2). IG1 participated in MindPower while IG2 served as a control group for four months until the intervention started also in this group. IG1 and IG2 responded to questionnaires before and after the eight weeks course, at the start of the first and the second booster session, and at the five months follow up. Questionnaires, including online versions of the Hopkins Symptom Checklist (SCL-8) and the Reynolds Adolescent Depression Scale (RADS-2:SF), were administered to 1673 out of a total of 2384 students. SCL-levels were also compared with those from a large population study (UngData). Results According to mixed model analyses, SCL-8 and RADS-2:SF showed significant baseline differences between IG1 and IG2. In IG1 and IG2, both SCL-8 and RADS-2:SF showed a small but significant increase in mean scores throughout the study period, with markedly lower mean scores among boys. The SCL-levels were first lower for both girls and boys and then after the completion of MindPower the SCL-levels, equal to the SCL-levels in UngData. Conclusions No effects of the intervention were found. This large universal school-based trial suffered from considerable drop-out of participants. Experiences from implementation and evaluation of universal mental health promotion and preventive school interventions are thoroughly discussed, including, preparation, resources, support, time, realistic expectations, teacher selection and training, implementation, research designs and more. Several empirically based, practical advices are presented.

• Waraan, Luxsiya; Mehlum, Lars; Rognli, Erling W.; Czajkowski, Nikolai Olavi & Villabø, Marianne (2021). Associations between insecure attachment styles to parents and suicidal ideation in adolescents with depression. Scandinavian Journal of Child and Adolescent Psychiatry and Psychology. 9, p. 41–51. doi: 10.21307/sjcapp-2021-006. Full text in Research Archive Show summary

  Objective: Suicidal ideation and depressive symptoms are often interrelated in clinical settings. Insecure attachment may be a risk factor for suicidal ideation in depressed adolescents. To our knowledge, this study is the first to examine the association between self-reported insecure attachment styles to both parents and suicidal ideation in a clinical sample of adolescents with depression. Methods: Fifty clinically depressed adolescents (13-17 years, 84% girls) completed self-reported measures of suicidal ideation, depressive symptoms, and attachment style to parents. Results: There was a statistically significant bivariate association between higher levels of attachment anxiety in relation to mothers and fathers and higher levels of suicidal ideation. When attachments to both parents were included in the same multivariate model, only attachment anxiety to the mother was significantly associated with the level of suicidal ideation. Self-reported depressive symptoms remained significantly associated with the level of suicidal ideation in all analyses. Younger adolescents with attachment anxiety reported higher levels of suicidal ideation than older adolescents. Conclusion: Conclusions about directionality and causality of associations between insecure attachment and suicidal ideation are limited due to the cross-sectional design. Our findings suggest that attachment anxiety in relation to the mother and father is associated with increased levels of suicidal ideation. Implication of these findings for treatment selection is discussed.

• Glad, Kristin Alve; Stensland, Synne; Czajkowski, Nikolai Olavi; Boelen, Paul & Dyb, Grete Anita (2021). The Longitudinal Association Between Symptoms of Posttraumatic Stress and Complicated Grief: A Random Intercepts Cross-Lag Analysis. Psychological Trauma. ISSN 1942-9681. doi: 10.1037/tra0001087. Full text in Research Archive
• Waraan, Luxsiya; Rognli, Erling W.; Czajkowski, Nikolai Olavi; Villabø, Marianne & Mehlum, Lars (2021). Effectiveness of attachment-based family therapy compared to treatment as usual for depressed adolescents in community mental health clinics. Child and Adolescent Psychiatry and Mental Health (CAPMH). 15, p. 1–14. doi: 10.1186/s13034-021-00361-x. Full text in Research Archive Show summary

  Background Major Depressive Disorder (MDD) is a disabling mood disorder, profoundly affecting a large number of adolescent’s quality of life. To date, no obvious treatment of choice for MDD in adolescents is available and progress in the treatment of depressed adolescents will have important public health implications. Attachment-Based Family Therapy (ABFT), as the only empirically supported family therapy model designed to treat adolescent depression, aims to repair interpersonal ruptures and rebuild an emotionally protective parent–child relationship. Objective To study the effectiveness of ABFT compared with treatment as usual (TAU) delivered within child- and adolescent mental health services (CAMHS) to adolescents with MDD. Method Sixty adolescents (86.7% girls), aged 13–18 years (M = 14.9, SD = 1.35), with MDD referred to two CAMHS were randomized to 16 weeks of ABFT or TAU. ABFT consisted of weekly therapy sessions (family/individual or both) according to the treatment manual. TAU was not monitored. Primary outcomes were assessed by blinded evaluators at baseline and post-treatment with the Hamilton Depression Scale (HAMD). Self-reported (Beck Depression Inventory-II, BDI-II) depressive symptoms were assessed at baseline, and after 4, 6, 8, 10,12, 14, and 16 weeks. Analyses were performed according to intent-to-treat principles. Results At post-treatment, clinician-rated remission rates on the HAMD (5% in ABFT and 3.33% in TAU, p = 1, OR = 1.54, Fisher’s exact test) and self-reported symptoms of depression on the BDI-II did not differ significantly between groups (X2[2, N = 60] = 0.06, p = 0.97). In both treatment groups participants reported significantly reduced depressive symptoms, but the majority (63.3%) of adolescents were still in the clinical range after 16 weeks of treatment. Conclusion ABFT was not superior to TAU. Remission and response rates were low in both groups, suggesting none of the treatments were effective in treating MDD in adolescents. Findings must be viewed in the context of the study’s small sample size, missing data, and implementation challenges. Continued efforts to improve treatment for MDD in outpatient clinics are warranted. Future research should examine moderators of and mechanisms for individual differences to treatment response, as well as the feasibility and cost-effectiveness of implementing treatment models which may require extensive training and expertise to yield clinically meaningful improvements in non-research settings. Trial registration Clinicaltrials.gov identifier: NCT01830088 https://clinicaltrials.gov/ct2/show/NCT01830088?term=Villab%C3%B8&draw=2&rank=1 Date of registration: April 12, 2013

• Askim, Kine; Czajkowski, Nikolai Olavi & Knardahl, Stein (2021). Exploring dynamic relationships between employees’ personalities and psychosocial work factors. European Journal of Work and Organizational Psychology. ISSN 1359-432X. 31(1). doi: 10.1080/1359432X.2021.1912016. Full text in Research Archive Show summary

  The current study addresses the potentially dynamic relationship between employees’ personality and their working conditions. A six-year full-panel longitudinal study of employed individuals was used to test whether (I) task-related, (II) social and (III) organizational work factors contribute to change Big-Five personality traits over time and whether personalities change working conditions. Bivariate latent change score analyses were conducted on repeated-measures data (four waves) from 2356 Norwegian employees. The results showed that specific work factors pertaining to task-related and social characteristics (i.e. leadership) were associated with personality trait changes. Contrary to our expectations, none of the work factors predicted change in neuroticism and extraversion, and we offer several possible explanations for these findings. The results also showed that all personality traits may play an active role in shaping specific attributes of the work environment over time and thereby shed light on how employees’ working conditions emerge.

• Ulset, Vidar; Czajkowski, Nikolai Olavi; Staton, Sally; Smith, Simon C.; Pattinson, Cassandra & Allen, Alicia [Show all 8 contributors for this article] (2021). Environmental Light Exposure, Rest-Activity Rhythms, and Symptoms of Inattention and Hyperactivity: An Observational Study of Australian Preschoolers. Journal of Environmental Psychology. ISSN 0272-4944. doi: 10.1016/j.jenvp.2021.101560. Full text in Research Archive
• Rognli, Erling W.; Aalberg, Marianne & Czajkowski, Nikolai Olavi (2020). Using informant discrepancies in report of parent–adolescent conflict to predict hopelessness in adolescent depression. Clinical Child Psychology and Psychiatry. ISSN 1359-1045. 26(1), p. 96–109. doi: 10.1177/1359104520969761. Full text in Research Archive Show summary

  Hopelessness is an important symptom of adolescent depression, being associated with both risk of suicide and poor treatment response, but predictors of hopelessness are understudied. Conflict with parents is common in adolescent depression, but parents and adolescents often disagree when reporting conflict severity. Discrepancy in reporting may be an indicator of the parent–adolescent dyad lacking a shared representation of the state of their relationship. This could make conflicts seem unresolvable to the adolescent, leading to expectations of persistent stress and lack of support, increasing hopelessness. This study employed latent difference scores, ordinal regression and cross-validation to evaluate the hypothesis that discrepancy in report of parent–adolescent conflict would predict hopelessness among depressed adolescents. Parents reporting less conflict than the adolescent was associated with increased adolescent hopelessness, giving preliminary support to the hypothesis.

• Gjerdevik, Miriam; Gjessing, Håkon K.; Romanowska, Julia; Haaland, Øystein Ariansen; Jugessur, Astanand & Czajkowski, Nikolai Olavi [Show all 7 contributors for this article] (2020). Design efficiency in genetic association studies. Statistics in Medicine. ISSN 0277-6715. 39, p. 1292–1310. doi: 10.1002/sim.8476. Full text in Research Archive Show summary

  Selecting the best design for genetic association studies requires careful deliberation; different study designs can be used to scan for different genetic effects, and each design has its own set of strengths and limitations. A variety of family and unrelated control configurations are amenable to genetic association analyses, including the case‐control design, case‐parent triads, and case‐parent triads in combination with unrelated controls or control‐parent triads. Ultimately, the goal is to choose the design that achieves the highest statistical power using the lowest cost. For given parameter values and genotyped individuals, designs can be compared directly by computing the power. However, a more informative and general design comparison can be achieved by studying the relative efficiency, defined as the ratio of variances of two different parameter estimators, corresponding to two separate designs. Using log‐linear modeling, we derive the relative efficiency from the asymptotic variance of the parameter estimators and relate it to the concept of Pitman efficiency. The relative efficiency takes into account the fact that different designs impose different costs relative to the number of genotyped individuals. We show that while optimal efficiency for analyses of regular autosomal effects is achieved using the standard case‐control design, the case‐parent triad design without unrelated controls is efficient when searching for parent‐of‐origin effects. Due to the potential loss of efficiency, maternal genes should generally not be adjusted for in an initial genome‐wide association study scan of offspring genes but instead checked post hoc. The relative efficiency calculations are implemented in our R package Haplin.

• Glad, Kristin Alve; Czajkowski, Nikolai Olavi; Dyb, Grete & Hafstad, Gertrud Sofie (2020). Does event centrality mediate the effect of peritraumatic reactions on post-traumatic growth in survivors of a terrorist attack? European Journal of Psychotraumatology. 11(1). doi: 10.1080/20008198.2020.1766276. Full text in Research Archive Show summary

  Background While self-reported post-traumatic growth (PTG) has been documented after a wide variety of potentially traumatic experiences, we need more knowledge on the mechanisms behind PTG to gain a better understanding of this phenomenon. Objective We aimed to investigate the hypothesized mechanism of perceived event centrality as a mediator on the pathway between peritraumatic reactions and later PTG. Method In total, 204 survivors of the 2011 massacre on Utøya island, participated 4–5 months (T1), 14–15 months (T2), and 30–32 months (T3) post-terror. We applied counterfactually based causal mediation analysis to explore the potential mediating role of survivors’ perceived centrality (T2) in linking their peritraumatic reactions (T1) and self-reported PTG (T3). Results The vast majority of the survivors reported experiencing some positive changes post-terror, and we found a positive, significant association between survivor’s peritraumatic reactions, perceived event centrality and self-reported growth. However, we did not find that centrality significantly mediated the longitudinal association between peritraumatic reactions and later PTG. Conclusion Reports of PTG are common post-terror, and peritraumatic reactions and perceptions of centrality may help explain individual differences in trauma survivors’ level of PTG. Perceived event centrality about one year post-trauma does not appear to explain the relationship between initial reactions to trauma and subsequent PTG.

• Czajkowski, Nikolai Olavi; Kendler, Kenneth S; Torvik, Fartein Ask; Ystrøm, Eivind; Rosenström, Tom Henrik & Gillespie, Nathan [Show all 7 contributors for this article] (2020). Caffeine consumption, toxicity, tolerance and withdrawal; shared genetic influences with normative personality and personality disorder traits. Experimental and clinical psychopharmacology. ISSN 1064-1297. doi: 10.1037/pha0000429. Full text in Research Archive
• Haukeland, Yngvild; Czajkowski, Nikolai Olavi; Fjermestad, Krister; Silverman, Wendy K.; Mossige, Svein & Vatne, Torun (2020). Evaluation of “SIBS”, An Intervention for Siblings and Parents of Children with Chronic Disorders. Journal of Child and Family Studies. ISSN 1062-1024. 29. doi: 10.1007/s10826-020-01737-x. Full text in Research Archive Show summary

  Siblings of children with chronic disorders are at increased risk of experiencing family communication problems and poorer mental health. We assessed initial feasibility, acceptability, and outcomes of SIBS; a manual-based group intervention for siblings and parents of children with chronic disorders, aiming to improve parent-sibling communication and sibling mental health. Ninety-nine siblings aged 8–16 years (M = 11.5 years, SD = 2.0; 54.5% girls) and parents (63.6% mothers) of children with chronic disorders participated in three separate group sessions for siblings and parents and two joint sessions with integrated sibling-parent dialogues. We assessed participant satisfaction post-intervention and checked for group leader manual adherence. We measured the following outcomes at baseline, three, and six months post-intervention in an open trial: (1) parent-sibling communication quality; (2) sibling emotional and behavioral problems; (3) sibling adaptation to the disorder; and (4) sibling disorder knowledge. Using growth curve modeling, we found significant improvement in parent-sibling communication quality (p = 0.001), emotional and behavioral problems (p = 0.009), adaptation to the disorder (p = 0.003), and disorder knowledge (p = 0.000) from baseline to follow-up (effect sizes d = 0.22 to 0.64). Improvement in sibling-reported emotional and behavioral problems and adaptation to the disorder was partly explained by communication quality. User satisfaction was high and manual adherence was good. Our evaluation yields support for the SIBS intervention, with initial evidence of acceptability, feasibility, and beneficial outcomes. Our study suggests targeting parent-sibling communication may be a beneficial way of improving siblings’ mental health.

• Siegel, Marte Langenes; Binder, Eva Mathilde Gullestad; Dahl, Hanne-Sofie Johnsen; Czajkowski, Nikolai Olavi; Critchfield, Kenneth L. & Høglend, Per Andreas [Show all 7 contributors for this article] (2020). Therapeutic Atmosphere in Psychotherapy Sessions. International Journal of Environmental Research and Public Health (IJERPH). ISSN 1661-7827. 17(11). doi: 10.3390/ijerph17114105. Full text in Research Archive Show summary

  There is uncertainty concerning what the active ingredients in psychotherapy are. The First Experimental Study of Transference interpretations (FEST) was a randomized controlled trial of the effects of transference work (TW) in psychodynamic psychotherapy. Women with low quality of object relations (QOR) showed a large positive effect of transference work, while men with high QOR showed a slight negative effect. The present study aimed to expand the knowledge from the FEST by investigating the therapeutic atmosphere with Structural Analysis of Social Behavior (SASB). Two-way ANOVAs were conducted to investigate differences between SASB cluster scores between subgroups. The therapeutic atmosphere was characterized by Protect-Trust, Affirm-Disclose and Control-Submit. Multilevel modeling was used to assess the relationship between a therapist variable and outcomes for men and women. Contrary to expectations, no significant differences in therapeutic atmosphere between subgroups (with or without TW in women with low QOR and men with high QOR) were observed using the process measure SASB.

• Rognli, Erling W.; Waraan, Luxsiya; Czajkowski, Nikolai Olavi & Villabø, Marianne (2020). Moderation of treatment effects by parent-adolescent conflict in a randomised controlled trial of Attachment-Based Family Therapy for adolescent depression. Scandinavian Journal of Child and Adolescent Psychiatry and Psychology. 8, p. 110–122. doi: 10.21307/sjcapp-2020-011. Full text in Research Archive Show summary

  Background: Conflict with parents is frequent in adolescent depression, and has been shown to predict poor treatment outcomes. Attachment Based Family Therapy (ABFT) is a manualised treatment for adolescent depression that may be robust to parent-adolescent conflict. Objective: To evaluate the hypothesis that parent-adolescent conflict moderates the outcome of Attachment-Based Family Therapy compared with treatment as usual. Methods: Data were obtained from a randomised trial comparing 16 weeks of ABFT to treatment as usual, in Norwegian Child and Adolescent Mental Health Services. Sixty adolescents with moderate to severe depression and their parents were recruited. Change in Grid-Hamilton Depression Rating Scale scores from baseline to week 16 was modelled using linear mixed models, and a three-way interaction of time, treatment allocation and a continuous measure of parent-adolescent conflict was fitted to estimate a moderator effect. The moderator model was compared to simpler models using leave-one-out cross-validation. Results: Better outcomes were predicted for Attachment-Based Family Therapy at high levels of mother-adolescent conflict, and for treatment as usual at low levels of mother-adolescent conflict, giving preliminary support to the moderator hypothesis. Findings for father-adolescent conflict were mixed. Cross-validation did not clearly support the moderator model over a simple effect of time, indicating that the replicability of these findings is uncertain. Conclusion: The results suggest that parent-adolescent conflict should be further studied as a moderator of outcome in Attachment-Based Family Therapy. The trial did not meet its recruitment target and had high attrition, limiting the conclusions that may be drawn.

• Waraan, Luxsiya; Rognli, Erling W.; Czajkowski, Nikolai Olavi; Mehlum, Lars & Villabø, Marianne (2020). Efficacy of attachment-based family therapy compared to treatment as usual for suicidal ideation in adolescents with MDD. Clinical Child Psychology and Psychiatry. ISSN 1359-1045. doi: 10.1177/1359104520980776. Full text in Research Archive Show summary

  Attachment-Based Family Therapy (ABFT) is the only empirically supported family therapy model designed to treat adolescent depression, including those at risk for suicide, and their families. ABFT aims to repair interpersonal ruptures and rebuild an emotionally protective parent-child relationship. To study the effectiveness of ABFT compared with Treatment as Usual (TAU) in reducing suicidal ideation in clinically depressed adolescents. Sixty adolescents (86.7% girls), aged 13 to 18 years ( M = 14.9), with major depressive disorder referred to two CAMHS were randomized to receive 16 weeks of ABFT or TAU. ABFT consisted of weekly therapy sessions according to the treatment manual. Suicidal ideation was measured with the Suicidal Ideation Questionnaire-Junior at 4, 6, 8, 10, 12, 14, and 16 weeks. Linear mixed models were fitted to test our hypothesis, time was the only factor to have a significant effect on suicidal ideation t(31.05) = −3.32, p &lt; .01. Participants in both treatment groups reported significantly reduced suicidal ideation, but the majority were still in the clinical range after 16 weeks of treatment. ABFT was not associated with more favorable outcomes than TAU. Findings must be interpreted with caution given the study limitations.

• Rognli, Erling Wright; Waraan, Luxsiya; Czajkowski, Nikolai Olavi; Solbakken, Ole Andre & Aalberg, Marianne (2020). Conflict with Parents in Adolescent Depression: Associations with Parental Interpersonal Problems and Depressive Symptoms. Child Psychiatry and Human Development. ISSN 0009-398X. 51, p. 442–452. doi: 10.1007/s10578-020-00955-0. Full text in Research Archive Show summary

  Conflict with parents is common among depressed adolescents, interferes with treatment, and may increase risk of recurrence. Parental depressive symptoms have been shown to predict conflict with adolescent children, but an important role for different kinds of parental interpersonal problems, as described by interpersonal circumplex, is also plausible. This study compared parental interpersonal problems to parental depressive symptoms as predictors of parent-adolescent conflict reported by a depressed adolescent child, using multilevel linear regression, leave-one-out cross-validation and model stacking (N = 100 parents, 57 mothers and 43 fathers, of 60 different adolescents). Cross-validation and model stacking showed that including parental interpersonal problems contributes to accurate predictions. Parents reporting more interpersonal problems related to excessive dominance or submissiveness was associated with increased or decreased conflict, respectively. Parental depressive symptoms were found to be negatively associated with parent-adolescent conflict only in father-adolescent relationships.

• Eilertsen, Espen Moen; Hannigan, Laurie John; McAdams, Tom A.; Rijsdijk, Frühling V.; Czajkowski, Nikolai Olavi & Reichborn-Kjennerud, Ted [Show all 8 contributors for this article] (2020). Parental Prenatal Symptoms of Depression and Offspring Symptoms of ADHD: A Genetically Informed Intergenerational Study. Journal of Attention Disorders. ISSN 1087-0547. April 26(April). doi: 10.1177/1087054720914386. Full text in Research Archive

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• Nes, Ragnhild Bang; Røysamb, Espen; Czajkowski, Nikolai Olavi & Prydz, Monica Beer (2026). Digital Wellbeing Promotion in the General Population: Effects, Mechanisms, and Long-Term Outcomes of the Five Ways to Wellbeing for All Intervention. Full text in Research Archive Show summary

  Introduction The global rise in mental health problems and compromised wellbeing highlights the need for scalable and cost-effective wellbeing interventions. The Five Ways to Wellbeing for All (5waysA) is a digital adaptation of the UK’s Five Ways to Wellbeing framework, promoting wellbeing through five activity domains: connect, be active, take notice, keep learning, and give. Delivered via two webinars and SMS reminders over ten weeks, the 5waysA program aims to enhance wellbeing and reduce psychological distress in the general population. Methods A large-scale randomized controlled trial (N = 969) and subsequent secondary analyses were conducted in Norway. Self-reported life satisfaction, flourishing, positive emotions, anxiety, and depression were assessed pre-, mid-, and post-intervention. Analyses included multilevel modeling, mediation analysis, and network intervention analysis (NIA). A 12-month follow-up study with synthetic control comparison examined long-term effects. Findings Compared to waiting-list controls, participants in the intervention group reported significantly greater improvements in wellbeing (life satisfaction, flourishing, positive emotions) and reductions in anxiety and depressive symptoms (Cohen’s d = 0.20–0.49), with larger effects among those with most pre-intervention symptoms. Mediation analyses indicated that engagement in the Five Ways activities partially explained these effects, with a clear dose–response relationship between activity engagement and wellbeing outcomes. NIA revealed that increased positive emotions represented the main direct pathway, linking the intervention to improved wellbeing. Long-term follow-up demonstrated sustained gains in life satisfaction at 12 months (d = 0.28), exceeding simulated population-level controls (d = 0.17). Conclusions The 5waysA program effectively promotes wellbeing and reduces distress through accessible, evidence-based activities. Its digital, low-cost format, and durable effects make it a promising large-scale strategy for population-level mental health promotion and positive psychological functioning.

• Yang, Tianfang; Anderson, Jacob; Corley, Robin; Hopfer, Christian; McGue, Matt & Rhee, Soo [Show all 10 contributors for this article] (2026). Linking Pathological Personality Trait to Parenting, Romantic Relationship, and Workplace Behaviors: Using Co-Twin Control to Understand Variances in Pathways. Full text in Research Archive
• Yang, Tianfang; Anderson, Jacob E.; Corley, Robin P.; Hopfer, Christian J.; McGue, Matt K. & Rhee, Soo [Show all 11 contributors for this article] (2026). Etiologic Links Between Personality Pathology and Workplace Behavior. Full text in Research Archive
• Yang, Tianfang; Anderson, Jacob E.; Corley, Robin P.; Hopfer, Christian J.; McGue, Matt K. & Rhee, Soo [Show all 11 contributors for this article] (2026). Linking pathological personality trait to workplace behaviors: using co-twin control to understand pathways. Full text in Research Archive
• Yang, Tianfang; Nikolic, Milena; Grønnerød, Cato & Czajkowski, Nikolai Olavi (2026). A Person-Centered Examination on the Overlap Between Maladaptive and Normal Personality Profiles: Evidence from Norwegian Community Sample. Full text in Research Archive
• Høstmælingen, Andreas Teisner; Nissen-Lie, Helene, Amundsen; Monsen, Jon Trygve; Heinonen, Erkki; Wampold, Bruce E. & Czajkowski, Nikolai Olavi [Show all 8 contributors for this article] (2026). The Potential Impact of Antidepressant Medication on Psychotherapy Outcome for Depressed Patients. Full text in Research Archive Show summary

  Aim: Many depressed patients are already being treated with antidepressant medication (ADM) when presenting for psychotherapy. However, the potential impact of ADM on psychotherapy processes and outcome remains an unresolved issue. A large body of research indicates a combination of ADM and psychotherapy is superior to either monotherapy, but there are also indications that especially long-term use of ADM may be associated with negative consequences such as tolerance, negative side effects and iatrogenic comorbidity. The aim of this study was to investigate changes in depressive symptoms and interpersonal problems for ADM users and non-medicated depressed patients during psychotherapy and follow-up. Methods: Depressive symptoms (SCL-90-R) were assessed on 11 occasions for 166 depressed patients. ADM was used by 50.6% of the sample while 49.4% were unmedicated. Change during treatment and follow-up was assessed with multilevel modeling. We assessed whether ADM predicted differences in symptom development. Results: Depressive symptoms significantly reduced at a rate of .05 per month in treatment (p <.001), corresponding to an effect size of 1.35. There was no significant difference between ADM users and nonmedicated patients at baseline. ADM users had nearly twice as long treatment duration than nonmedicated patients, and ADM users had lower rate of symptom reduction than nonmedicated patients for depressive symptoms. Conclusions: Our results indicate medicated patients experience less response to psychotherapy than non medicated. Patients on ADM may believe that depression is primarily a biochemical condition and thus have less confidence in the potential for psychotherapy to treat depression. Also, it is possible that patients not using ADM have better access to emotions that need to be accessed and processed in psychotherapy. Iatrogenic comorbidity may thus have contributed to slower improvement for ADM users.

• Solbakken, Siri Marie; Riemann, Sebastian; Page, Christian Magnus; Holvik, Kristin; Kuiper, Lieke M & Czajkowski, Nikolai Olavi [Show all 12 contributors for this article] (2026). Reduced pain tolerance in asthma and COPD: the Tromsø and Rotterdam studies. Scandinavian Journal of Pain. ISSN 1877-8860. 26(1), p. eA4–eA5. doi: https:/www.degruyterbrill.com/document/doi/10.1515/sjpain-2026-0013/html. Full text in Research Archive
• Yang, Tianfang; Eftedal, Nikolai Haahjem; Valstad, Mathias; Reichborn-Kjennerud, Ted; Ystrom, Eivind & Czajkowski, Nikolai Olavi (2025). The lifespan impact of personality disorder on marital outcome: a Norwegian population study. Full text in Research Archive
• Czajkowski, Nikolai Olavi; Gustavson, Kristin & Ystrom, Eivind (2025). When Dracula Takes the PID-5: What Can We Learn from Psychometric Exploration of Data Simulated Using Large Language Models. Full text in Research Archive Show summary

  Several recent studies have demonstrated that large language models (LLMs) are able to simulate responses to surveys in ways that mimic observed characteristics of data from real human samples (Argyle, 2023). Since LLMs are trained on a sizeable proportion of all text produced by humans, it is reasonable to expect that they capture a deep understanding of human personality traits. Consequently, analysing data simulated by LLM’s may enable new ways to study psychological constructs and develop psychometric instruments. In this exploratory study, we used the GPT programming interface (API) to prompt the model to generate responses for 300 well-known literary characters across several instruments related to pathological and normative personality traits. This included the PID-5, the Structured Interview for DSM-5 Personality Disorders (SIDP), the Big Five Inventory-2 (BFI-2), and the IPIP-300. Characters were drawn from a wide range of literary traditions, genres, and historical periods. For each instrument, GPT-4o was instructed to adopt the voice and perspective of the character and provide item-level responses using standard Likert-style scales. Our goal was twofold: first, to assess whether the factor structures and inter-scale correlations observed in the simulated data resembled those from real-world samples; and second, to explore whether the same data might suggest novel trait constellations or latent domains not fully captured by existing instruments. Together, these analyses offer a proof of concept for using LLMs in hypothesis generation and instrument development.

• Czajkowski, Nikolai Olavi; Solbakken, Ole Andre; Stenberg, Jan-Henry; Suoma, Saarni E. & Rosenström, Tom Henrik (2025). Evaluating Internet-Based CBT for Depression in Patients with Prior Borderline Personality Disorder: Evidence from Finnish Registry Data. Full text in Research Archive Show summary

  Internet-based cognitive behavioral therapy (iCBT) has demonstrated comparable effectiveness to traditional psychotherapy for mild to moderate depression, as shown in a recent large-scale Finnish registry study (Rosenström et al., 2025). In routine care, patients with comorbid borderline personality disorder (BPD) are often referred to more intensive treatment formats, and registry data suggest they receive significantly more psychotherapy sessions than individuals with depression alone, even when symptom severity is comparable (van Bronswijk et al., 2021). Findings such as this may contribute to clinicians hesitating to offer low-intensity treatments, such as iCBT, to patients with current or prior BPD diagnoses. However, to our knowledge, no studies have directly assessed whether a history of BPD is associated with reduced effectiveness of iCBT for depression. In this study, we will use data from the HUS-iCBT registry and the Finnish Psychotherapy Quality Register (FPQR) to investigate whether: A BPD diagnosis (ICD-10 F60.3) moderates the effectiveness of iCBT for depression. Conventional face-to-face CBT (fCBT) yields superior outcomes for patients with prior BPD compared to iCBT. BPD is associated with increased dropout in iCBT. Our analyses will focus on patients diagnosed with mild to moderate depressive episodes (ICD-10 F32.0–F32.1), with symptom severity assessed using the PHQ-9 or BDI. Linear mixed-effects models will test for moderation effects, compare outcomes between iCBT and fCBT, and examine dropout patterns by diagnostic subgroup.

• Valstad, Mathias; Eftedal, Nikolai Haahjem; Yang, Tianfang; Reichborn-Kjennerud, Ted; Ystrom, Eivind & Czajkowski, Nikolai Olavi (2025). Epidemiology of personality disorders in Norway, 2010 to 2022. Full text in Research Archive
• Krogshus, Kristian Green; Bjertness, Espen; Czajkowski, Nikolai Olavi; Rodriguez-Cano, Ruben & Nes, Ragnhild Bang (2025). Study protocol for 5Ways@School – An implementation and effectiveness trial of a school-based wellbeing intervention in 16 schools in Norway. doi: 10.1177/14034948251370109. Full text in Research Archive Show summary

  Aims: This study aims to assess the effectiveness and implementation of the 5Ways@School curriculum-based intervention in Norwegian schools. The intervention builds on the Five Ways to Wellbeing framework, and promotes five action domains: connect with others, be physically active, take notice, keep learning, and give. The study objectives include assessing the intervention’s acceptability, appropriateness, feasibility, fidelity, and cost, as well as its impact on students’ wellbeing and mental health. Methods: The study is a hybrid effectiveness–implementation trial using mixed methods. It is a longitudinal, two-armed, non-randomized, controlled study involving students in grades 5 to 10 (ages 10 to 16). The primary outcomes are the intervention’s acceptability and feasibility, and its effectiveness on students’ wellbeing. Data collection includes web-based questionnaires for students and teachers, and qualitative interviews with teachers. Quantitative data will be analysed using multilevel regression models and network intervention analysis, while qualitative data will be analysed using thematic analysis. Conclusions: The study aims to provide insights into the implementation and effectiveness of the wellbeing-promoting 5Ways@School intervention. The findings could inform the optimization of the 5Ways@School and other future school-based interventions, and thereby contribute to the wellbeing of children and young people. The study’s strengths include its real-life school setting and mixed methods approach, while limitations include its non-randomized design. Trial registration: ClinicalTrials.gov, ID NCT06144502.

• Czajkowski, Nikolai Olavi; Eilertsen, Espen Moen; Valstad, Mathias; Eftedal, Nikolai Haahjem & Ystrøm, Eivind (2025). A Bayesian Framework for Zygosity Classification and Heritability Estimation Using Nationwide Registry Data. Full text in Research Archive
• Czajkowski, Nikolai Olavi (2025). Kan kunstig intelligens være empatisk? Tidsskrift for Den norske legeforening (Tidsskriftet). ISSN 0029-2001. 145(2), p. 117–117. doi: 10.4045/tidsskr.25.0044. Full text in Research Archive
• Yang, Tianfang; Ystrøm, Eivind; Valstad, Mathias; Eftedal, Nikolai Haahjem; Reichborn-Kjennerud, Ted & Czajkowski, Nikolai Olavi (2025). Marital Consequence of Personality Disorder: Evidence from Norwegian Registry. Full text in Research Archive
• Yang, Tianfang; Ystrøm, Eivind; Valstad, Mathias; Eftedal, Nikolai Haahjem; Reichborn-Kjennerud, Ted & Krueger, Robert F [Show all 7 contributors for this article] (2024). The Intergenerational Impact of Borderline and Avoidant Personality Disorders on Child Academic Achievement: A Registry Study in Norway. Full text in Research Archive
• Czajkowski, Nikolai Olavi; Eftedal, Nikolai Haahjem; Yang, Tianfang; Valstad, Mathias; Reichborn-Kjennerud, Ted & Ystrøm, Eivind (2024). The Role of Parental Personality Disorders in High School Dropout: Insights from a Nationwide Cohort Study. Full text in Research Archive
• Valstad, Mathias; Eilertsen, Espen Moen; Timpe, Clara Marie Fides; Yang, Tianfang; Eftedal, Nikolai Haahjem & Reichborn-Kjennerud, Ted [Show all 8 contributors for this article] (2024). Genetic and environmental effects on diagnosed Borderline Personality Disorder (BPD) without clinic bias. Full text in Research Archive
• Yang, Tianfang; Ystrøm, Eivind; Valstad, Mathias; Eftedal, Nikolai Haahjem; Reichborn-Kjennerud, Ted & Czajkowski, Nikolai Olavi (2024). Parental Personality Disorder, Substance Abuse and Child Academic Performance: a Norwegian Registry Study. Full text in Research Archive
• Eftedal, Nikolai Haahjem; Eilertsen, Espen Moen; Sunde, Hans Fredrik; Kleppestø, Thomas Haarklau; Ystrøm, Eivind & Czajkowski, Nikolai Olavi (2023). Correlations on Norwegian national standardized tests between millions of pairs of relatives: Exploring the impacts of assortative mating and parental effects. Full text in Research Archive
• Krogshus, Kristian Green; Bjertness, Espen; Czajkowski, Nikolai Olavi; Nes, Ragnhild Bang & Rodriguez-Cano, Ruben (2023). 5 Ways to Promote Wellbeing @School. Full text in Research Archive
• Smajlagic, Dinka; Tsotsi, Stella; Gjerdevik, Miriam; Page, Christian Magnus; Zayats, Tetyana & Austerberry, Chloe [Show all 14 contributors for this article] (2022). Parent-of-origin effects in childhood aggression. Full text in Research Archive
• Nes, Ragnhild Bang; Czajkowski, Nikolai Olavi; Røysamb, Espen & Eilertsen, Maja Gunvor (2022). Promoting wellbeing and preventing mental health problems: A randomized controlled trail of the Five Ways to All Intervention. Full text in Research Archive
• Nes, Ragnhild Bang; Røysamb, Espen; Eilertsen, Maja Gunvor & Czajkowski, Nikolai Olavi (2022). Promoting Wellbeing using the Five Ways to Wellbeing framework. Full text in Research Archive
• Eilertsen, Maja; Nes, Ragnhild Bang; Prydz, Monica Beer; Røysamb, Espen & Czajkowski, Nikolai Olavi (2022). Bridging the gap - from research to practice. Full text in Research Archive
• Eilertsen, Maja Gunvor; Nes, Ragnhild Bang; Røysamb, Espen & Czajkowski, Nikolai Olavi (2022). Fem grep for økt Hverdagsglede på tvers av nivåer. Full text in Research Archive
• Eilertsen, Maja; Nes, Ragnhild Bang; Czajkowski, Nikolai Olavi; Røysamb, Espen & Prydz, Monica Beer (2022). Promoting Wellbeing using the Five Ways to Wellbeing framework. Full text in Research Archive
• Eilertsen, Maja; Nes, Ragnhild Bang; Czajkowski, Nikolai Olavi; Røysamb, Espen; Ørstavik, Ragnhild & Vassend, Olav Mandt (2022). Effects of illness on wellbeing: A co-twin control analysis. Full text in Research Archive
• Prydz, Monica Beer; Czajkowski, Nikolai Olavi; Eilertsen, Maja & Nes, Ragnhild Bang (2022). Helsekompetansens kraft i folkehelsearbeidet. Hvordan kan helsekompetanse innlemmes i folkehelsearbeid? Full text in Research Archive
• Prydz, Monica Beer; Czajkowski, Nikolai Olavi; Nes, Ragnhild Bang; Røysamb, Espen & Eilertsen, Maja (2022). Promoting wellbeing and preventing mental health problems: A randomized controlled trail of the Five Ways to Wellbeing Intervention. Full text in Research Archive
• Tsotsi, Stella; Goh, shaun; Czajkowski, Nikolai Olavi; Smajlagic, Dinka; Coplan, Robert & Bølstad, Evalill [Show all 7 contributors for this article] (2022). The co-occurrence of emotional difficulties and aggression in early childhood and the risk of later mental health outcomes: The Norwegian Mother, Father and Child Cohort. Full text in Research Archive
• Mayerhofer, Lilian Juliane Kozlowski; Nes, Ragnhild Bang; Lan, Xiaoyu; Czajkowski, Nikolai Olavi; Ystrøm, Eivind & Røysamb, Espen (2022). Social support and wellbeing across the pre- and postnatal period in women victim of abuse: Findings from the Norwegian Mother, Father and Child Cohort Study. Full text in Research Archive
• Torgalsbøen, Anne Kari & Czajkowski, Nikolai Olavi (2022). Full recovery and self-efficacy in first episode schizophrenia: The OSR cohort at 10 year follow-up. Full text in Research Archive
• Glad, Kristin Alve; Stensland, Synne; Czajkowski, Nikolai Olavi; Boelen, Paul & Dyb, Grete (2020). The longitudinal association between symptoms of posttraumatic stress and complicated grief. A random intercepts cross-lag analysis. Full text in Research Archive
• Eilertsen, Maja; Omsland, Tone Kristin; Nes, Ragnhild Bang & Czajkowski, Nikolai Olavi (2026). Biopsychosocial outcomes of wellbeing-promoting interventions: when life wears you down. Universitetet i Oslo. ISSN 9788234808890. Full text in Research Archive Show summary

  Wellbeing-promoting interventions may help counteract the effect of stress across biological, psychological, and social domains, although the underlying mechanisms remain incompletely understood. Situated within public health and health promotion research, this thesis explored the potential of such interventions to improve wellbeing, health, social connection, and work participation, particularly among adults facing health and social challenges. The first study was a systematic review and meta-analysis of 25 randomized controlled trials examining the effects of positive psychology interventions on biological markers of stress, including inflammatory biomarkers and cortisol. The findings indicated a modest but significant effect on inflammatory biomarkers, supporting the view that wellbeing interventions may positively influence biological processes. The second study evaluated the Five Ways to Wellbeing course among 373 participants in municipal health services. Participation was associated with sustained improvements in wellbeing, social connection, and self-rated health. Mental health outcomes improved more than in a comparable group of 524 individuals receiving Healthy Life Centre services. The third study was a randomized controlled trial of the Five Ways to Wellbeing course among 171 adults receiving support from NAV. Although recruitment difficulties and attrition limited statistical power and precluded firm conclusions regarding effectiveness, the study highlighted the challenges of conducting intervention research in welfare settings. Overall, the findings support the view that wellbeing is a modifiable resource that may strengthen resilience to stress across biological, psychological, and social domains. The thesis highlights the potential of wellbeing-promoting interventions to improve biological as well as psychological and social outcomes, while underscoring the need for pragmatic research designs that can be implemented in health and welfare services.

• Rognli, Erling W.; Villabø, Marianne & Czajkowski, Nikolai Olavi (2020). Conflict with Parents in Adolescent Depression. Universitetet i Oslo. Full text in Research Archive
• Glad, Kristin Alve; Hafstad, Gertrud Sofie; Dyb, Grete & Czajkowski, Nikolai Olavi (2020). Transformed by trauma. A longitudinal study of posttraumatic stress, growth and perceived event centrality among youths and emerging adults after the terrorist attack on Utøya island. Damnett. Full text in Research Archive

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