Olav Mandt Vassend

• 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
• 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.

• 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.

• 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.

• 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.

• Bjørndal, Ludvig Daae; Nes, Ragnhild Bang; Ayorech, Ziada; Vassend, Olav Mandt & Røysamb, Espen (2024). Multiple social factors are associated with wellbeing when accounting for shared genetic and environmental confounding. Quality of Life Research. ISSN 0962-9343. doi: 10.1007/s11136-024-03832-8. Full text in Research Archive Show summary

  Purpose Social factors are associated with mental health and wellbeing. However, few studies have examined genetic and environmental influences on social factors themselves, limiting current understanding of influences on aspects of the social environment. Most studies which have identified links between social factors and mental health are also limited by the possible influence of unmeasured genetic and environmental confounding. In this study, we investigated the genetic and environmental underpinnings of multiple social factors (relationship satisfaction, loneliness, attachment, trust, relationship disruptions), and their associations with life satisfaction measured concurrently and six years later, after accounting for shared genetic and environmental confounding. Methods Data from a population-based sample of adult twins (N = 1987) and two measurement timepoints were used for the primary analyses. We used multivariate Cholesky models to estimate genetic and environmental influences across five social factors. Subsequently, we conducted co-twin control analyses to examine associations between social factors and wellbeing after controlling for shared genetic and environmental confounding. Results Heritability estimates for the social factors ranged from 24 to 42%. Genetic correlations across social factors were substantial, indicative of considerable genetic overlap. Associations between wellbeing and relationship satisfaction, loneliness, anxious and avoidant attachment, trust, and disruptions in relationships in the past year were attenuated in co-twin control analyses but remained statistically significant. Relationship satisfaction, loneliness, and attachment avoidance were also associated with wellbeing measured six years later in estimates which controlled for shared genetic and environmental confounding. Conclusion Our findings provide evidence that multiple social factors are associated with wellbeing after accounting for potential confounding by shared genetic and/or environmental factors. These findings highlight the importance of multiple aspects of the social environment for wellbeing in older adulthood. Future studies should examine the directionality in associations between social factors and mental health and assess these relationships beyond older adulthood.

• 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.

• 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.

• Hauge, Mariann Saanum; Storo, Bent; Vassend, Olav Mandt; Hoffart, Asle & Willumsen, Tiril (2022). Tannlegeadministrert kognitiv atferdsterapi versus «Fire gode vaner» – bruk av midazolam: En randomisert kontrollert studie av behandling av tannbehandlingsangst i primær tannhelsetjeneste. Den norske tannlegeforenings Tidende. ISSN 0029-2303. 132(8), p. 626–636. doi: 10.56373/2022-8-4. Full text in Research Archive
• Løke, Daniel; Andelic, Nada; Helseth, Eirik; Vassend, Olav Mandt; Andersson, Stein & Ponsford, Jennie [Show all 9 contributors for this article] (2022). Stability and Change in Biopsychosocial Factors Associated With Fatigue 6 and 12 Months After Traumatic Brain Injury: An Exploratory Multilevel Study. The journal of head trauma rehabilitation. ISSN 0885-9701. 38(4). doi: 10.1097/HTR.0000000000000847. Full text in Research Archive
• 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.

• Løke, Daniel; Løvstad, Marianne; Andelic, Nada; Andersson, Stein; Ystrøm, Eivind & Vassend, Olav Mandt (2022). The role of pain and psychological distress in fatigue: a co-twin and within-person analysis of confounding and causal relations. Health Psychology and Behavioral Medicine. 10(1), p. 160–179. doi: 10.1080/21642850.2022.2033121. Full text in Research Archive Show summary

  Objective: Fatigue is a common symptom in somatic and mental illness. Musculoskeletal pain and psychological distress have in turn frequently been shown to be associated with fatigue across clinical conditions and in the general population. The study aims to disentangle direct effects from those due to mere confounding from shared etiologies. Design: The study used genetically informative longitudinal twin data, through a co-twin control design with an additional within-person dimension. Methods: Data on fatigue, pain and distress from 2196 mono – and dizygotic twins from the Norwegian Twin Registry examined at two time points five years apart was analyzed using multilevel generalized linear regression modeling. Fatigue was regressed on pain and distress, with further controls added for confounding from genetic and stable non-shared environmental sources. Results: Pain and distress had a significant impact on fatigue at genetic, stable non-shared environmental and time-varying levels, even when controlling for somatic comorbidity. Conclusion: The findings indicate that a significant proportion of the association between fatigue, pain and distress is due to genetic and environmental confounding. Pain and distress exert significant, albeit smaller effects on fatigue even when controlling for genetic and stable environmental contributions, indicating direct effects. Potential etiological pathways and underlying mechanisms are discussed.

• Løke, Daniel; Andelic, Nada; Helseth, Eirik; Vassend, Olav Mandt; Andersson, Stein & Ponsford, Jennie L. [Show all 9 contributors for this article] (2022). Impact of Somatic Vulnerability, Psychosocial Robustness and Injury-Related Factors on Fatigue following Traumatic Brain Injury—A Cross-Sectional Study. Journal of Clinical Medicine. 11(6), p. 1–19. doi: 10.3390/jcm11061733. Full text in Research Archive Show summary

  Fatigue is a common symptom after traumatic brain injuries (TBI) and a crucial target of rehabilitation. The subjective and multifactorial nature of fatigue necessitates a biopsychosocial approach in understanding the mechanisms involved in its development. The aim of this study is to provide a comprehensive exploration of factors relevant to identification and rehabilitation of fatigue following TBI. Ninety-six patients with TBI and confirmed intracranial injuries were assessed on average 200 days post-injury with regard to injury-related factors, several patient-reported outcome measures (PROMS) of fatigue, neuropsychological measures, and PROMS of implicated biopsychosocial mechanisms. Factor analytic approaches yielded three underlying factors, termed Psychosocial Robustness, Somatic Vulnerability and Injury Severity. All three dimensions were significantly associated with fatigue in multiple regression analyses and explained 44.2% of variance in fatigue. Post hoc analyses examined univariate contributions of the associations between the factors and fatigue to illuminate the relative contributions of each biopsychosocial variable. Implications for clinical practice and future research are discussed.

• Hauge, Mariann Saanum; Stora, Bent; Vassend, Olav; Hoffart, Asle & Willumsen, Tiril (2021). Dentist-administered cognitive behavioural therapy versus four habits/midazolam: An RCT study of dental anxiety treatment in primary dental care. European Journal of Oral Sciences. ISSN 0909-8836. p. 1–12. doi: 10.1111/eos.12794. Full text in Research Archive Show summary

  The study aimed to test the effectiveness of cognitive behavioural therapy (CBT) administered by a general dental practitioner (GDP) in a general dental practice. In a two-arm parallel randomised controlled trial, the experimental group received a short dentist-administered CBT-intervention (D-CBT). A best-practice control group (FHM) received dental treatment during sedation with midazolam combined with an evidence-based communication model (The Four Habits Model). Ninety-six patients with self-reported dental anxiety were allocated to the treatment arms at a 1:1 ratio. Modified Dental Anxiety Scale (MDAS) scores spanned from 12 to 25, and 82 patients (85%) had a score of 19 or more, indicating severe dental anxiety. In both treatment arms, scores on MDAS and Index of Dental Anxiety and Fear (IDAF-4C) decreased significantly, but no differences were found between treatment arms. Mean reductions were: MDAS scores: −6.6 (SD = 0.5); IDAF-4C scores: −1.0 (SD = 1.1). In conclusion, local GDPs in general dental practices with proper competence have the ability for early detection of dental anxiety and, with the use of a manual-based D-CBT or FHM treatment, GDPs could offer efficient first-line treatment suitable for dental anxiety of varying severities.

• Melinder, Annika Maria D; Brennen, Timothy John; Husby, Mikael Falkhaugen & Vassend, Olav (2020). Personality, confirmation bias, and forensic interviewing performance. Applied Cognitive Psychology. ISSN 0888-4080. doi: 10.1002/acp.3674. Full text in Research Archive Show summary

  Confirmation bias is a universal characteristic of human cognition, with consequences for information processing and reasoning in everyday situations as well as in professional work such as forensic interviewing. Cognitive measures such as general intelligence are also related to personality traits, but there is a lack of research on personality and confirmation bias specifically. This study focuses, firstly, on the relationship between Big Five personality traits and confirmation bias as measured by the Wason selection task, and secondly, how these dispositions are related to observed performance in real forensic interviews of child victims. In a sample of police interviewers, Openness (i.e., the facets Ideas and Fantasy) and Neuroticism (i.e., the facets Anxiety and Vulnerability) were independently associated with confirmation bias (N = 72). Scores on the selection task, the Openness facet Values, and the Extraversion facets Assertiveness and Activity were consistently related to interview performance (N = 46). Implications of these findings are discussed for the empirical and conceptual relations of cognitive ability to personality and for the selection and training of police interviewers and their professional development.

• Kleppestø, Thomas Haarklau; Czajkowski, Nikolai Olavi; Vassend, Olav; Røysamb, Espen; Eftedal, Nikolai Haahjem & Sheehy-Skeffington, Jennifer [Show all 8 contributors for this article] (2019). Correlations between social dominance orientation and political attitudes reflect common genetic underpinnings. Proceedings of the National Academy of Sciences of the United States of America (PNAS). ISSN 0027-8424. 116(36), p. 17741–17746. doi: 10.1073/pnas.1818711116. Full text in Research Archive Show summary

  A foundational question in the social sciences concerns the interplay of underlying causes in the formation of people’s political beliefs and prejudices. What role, if any, do genes, environmental influences, or personality dispositions play? Social dominance orientation (SDO), an influential index of people’s general attitudes toward intergroup hierarchy, correlates robustly with political beliefs. SDO consists of the subdimensions SDO-dominance (SDO-D), which is the desire people have for some groups to be actively oppressed by others, and SDO-egalitarianism (SDO-E), a preference for intergroup inequality. Using a twin design (n = 1,987), we investigate whether the desire for intergroup dominance and inequality makes up a genetically grounded behavioral syndrome. Specifically, we investigate the heritability of SDO, in addition to whether it genetically correlates with support for political policies concerning the distribution of power and resources to different social groups. In addition to moderate heritability estimates for SDO-D and SDO-E (37% and 24%, respectively), we find that the genetic correlation between these subdimensions and political attitudes was overall high (mean genetic correlation 0.51), while the environmental correlation was very low (mean environmental correlation 0.08). This suggests that the relationship between political attitudes and SDO-D and SDO-E is grounded in common genetics, such that the desire for (versus opposition to) intergroup inequality and support for political attitudes that serve to enhance (versus attenuate) societal disparities form convergent strategies for navigating group-based dominance hierarchies.

• Vassend, Olav; Røysamb, Espen; Nielsen, Christopher Sivert & Czajkowski, Nikolai Olavi (2018). Fatigue symptoms in relation to neuroticism, anxiety-depression, and musculoskeletal pain. A longitudinal twin study. PLOS ONE. 13(6). doi: 10.1371/journal.pone.0198594. Full text in Research Archive Show summary

  Background: The nature of the relationship between fatigue and its risk factors is poorly understood. In the present study the genetic and environmental association between anxiety-depression, musculoskeletal (MS) pain and fatigue was examined, and the role of neuroticism as a shared risk factor that may possibly explain the co-occurrence between these phenotypes was investigated in a combined cross-sectional and longitudinal twin design. Methods: The sample consisted of 746 monozygotic (MZ) and 770 dizygotic (DZ) twins in the age group of 50–65 (mean = 57.11 years, SD = 4.5). Continuous measures of fatigue symptoms and the other phenotypes were employed. Using Cholesky modeling, genetic and environmental influences on the phenotypes, and the associations among them, were determined. Analyses were performed using measures of neuroticism obtained concurrently and 13–19 years earlier. Results: Results from multiple regression analyses showed that neuroticism, anxiety-depression symptoms, and MS pain were all significantly associated with fatigue, controlling for sex, education, and general health indices. The best-fitting biometric models included additive genetic and individual-specific environmental effects. Heritabilities in the 0.40–0.53 range were demonstrated. Furthermore, while there was a considerable overlap in genetic risk factors between the four phenotypes, a substantial proportion of the genetic risk shared between anxiety-depression and fatigue, and between MS pain and fatigue, was independent of neuroticism. Conclusion: Evidence for a common underlying susceptibility to report fatigue symptoms, genetically linked to neuroticism, anxiety-depression, and MS pain, was found. Both unique and pleiotropic effects appear to be involved in the genetic architecture of the phenotypes.

• Røysamb, Espen; Nes, Ragnhild Bang; Czajkowski, Nikolai Olavi & Vassend, Olav (2018). Genetics, personality and wellbeing. A twin study of traits, facets and life satisfaction. Scientific Reports. 8. doi: 10.1038/s41598-018-29881-x. Full text in Research Archive Show summary

  Human wellbeing is influenced by personality traits, in particular neuroticism and extraversion. Little is known about which facets that drive these associations, and the role of genes and environments. Our aim was to identify personality facets that are important for life satisfaction, and to estimate the contribution of genetic and environmental factors in the association between personality and life satisfaction. Norwegian twins (N = 1,516, age 50–65, response rate 71%) responded to a personality instrument (NEO-PI-R) and the Satisfaction With Life Scale (SWLS). Regression analyses and biometric modeling were used to examine influences from personality traits and facets, and to estimate genetic and environmental contributions. Neuroticism and extraversion explained 24%, and personality facets accounted for 32% of the variance in life satisfaction. Four facets were particularly important; anxiety and depression in the neuroticism domain, and activity and positive emotions within extraversion. Heritability of life satisfaction was 0.31 (0.22–0.40), of which 65% was explained by personality-related genetic influences. The remaining genetic variance was unique to life satisfaction. The association between personality and life satisfaction is driven mainly by four, predominantly emotional, personality facets. Genetic factors play an important role in these associations, but influence life satisfaction also beyond the effects of personality.

• Vassend, Olav; Røysamb, Espen; Nielsen, Christopher Sivert & Czajkowski, Nikolai Olavi (2017). Musculoskeletal Complaints, Anxiety–Depression Symptoms, and Neuroticism: A Study of Middle-Aged Twins. Health Psychology. ISSN 0278-6133. 36(8), p. 729–739. doi: 10.1037/hea0000484. Full text in Research Archive
• Vassend, Olav; Orvik, Benedicte Humborstad; Czajkowski, Nikolai Olavi & Røysamb, Espen (2016). Facets of neuroticism and musculoskeletal symptoms. A study of middle-aged twins. Norsk Epidemiologi. ISSN 0803-2491. 26(1-2), p. 47–56. doi: 10.5324/nje.v26i1-2.2015. Full text in Research Archive
• Bech, P.; Carrozzino, D.; Austin, Stephen F.; Møller, Silje Bakke & Vassend, Olav (2016). Measuring euthymia within the Neuroticism Scale from the NEO Personality Inventory: A Mokken analysis of the Norwegian general population study for scalability. Journal of Affective Disorders. ISSN 0165-0327. 193, p. 99–102. doi: 10.1016/j.jad.2015.12.039. Full text in Research Archive
• Carrozzino, Danilo; Vassend, Olav; Bjørndal, Flemming; Pignolo, Claudia; Olsen, Lis Raabæk & Bech, Per (2016). A clinimetric analysis of the Hopkins Symptom Checklist (SCL-90-R) in general population studies (Denmark, Norway, and Italy). Nordic Journal of Psychiatry. ISSN 0803-9488. 70(5), p. 374–379. doi: 10.3109/08039488.2016.1155235. Full text in Research Archive
• Vassend, Olav (2015). Personlighetstrekk i relasjon til psykisk og fysisk helse. In Kennair, Leif Edward Ottesen & Hagen, Roger (Ed.), Personlighetspsykologi. Fagbokforlaget. ISSN 9788245017151. p. 191–217. Full text in Research Archive
• Vassend, Olav; Røysamb, Espen & Nielsen, Christopher Sivert (2013). Five-factor personality traits and pain sensitivity: A twin study. Pain. ISSN 0304-3959. 154(5), p. 722–728. doi: 10.1016/j.pain.2013.01.010. Full text in Research Archive
• Mohn, Christine; Vassend, Olav & Knardahl, Stein (2012). Cardiovascular responses to and modulation of pressure pain sensitivity in normotensive, pain-free women. Scandinavian Journal of Pain. ISSN 1877-8860. 3(3), p. 165–169. doi: 10.1016/j.sjpain.2011.12.001. Full text in Research Archive Show summary

  Background and purpose: The psychophysiological responses to and modulation of pressure pain stimulation are relatively new areas of investigation. The aims of the present study were to characterize subjective and cardiovascular (CV) responses to pressure pain stimulation, and to examine the relationship between CV responding and pain pressure pain sensitivity. Methods: Thirty-nine pain-free, normotensive women were included in the study and tested during the follicular phase of their menstrual cycles. Pain threshold and tolerance were recorded at the right masseter muscle and the sternum, and visual analogue scales (VAS) were used to rate both pain intensity (the sensory dimension) and discomfort (the affective dimension). Mean arterial pressure (MAP), heart rate (HR), and facial and digital skin blood flux (SBF) were registered continuously. Results: The pain threshold and tolerance were significantly higher at the sternum compared with the masseter, but the level of affective distress was higher at the masseter tolerance point. No associations emerged between pressure pain threshold and tolerance stimulation levels, and the corresponding VAS ratings. Pressure pain stimulation of the masseter induced significant increases in MAP, HR, and a decrease in digital SBF. During sternum pressure stimulation a significant change in HR and digital SBF was observed. There were no significant correlations between CV responding and pressure pain sensitivity. Conclusion: Healthy women seem to display higher pressure pain sensitivity at the masseter region relative to the sternum. Pressure pain stimulation was associated with significant changes in MAP, HR, and SBF, but was not modulated by CV responses. The validity of these findings is strengthened by our control for menstrual cycle events, weekend-related changes in physiology, and CV changes during pain stimulation. Implications: This study extends previous reports of SBF sensitivity to electrocutaneous pain into the field of pressure stimulation. Moreover, this study suggests that the often demonstrated association between high BP and low pain sensitivity may not apply to pressure pain specifically. Alternatively, this finding adds to the literature of gender differences in the relationship between CV responding and acute pain sensitivity in general.

• Vassend, Olav; Røysamb, Espen & Nielsen, Christopher Sivert (2012). Neuroticism and self-reported somatic health: A twin study. Psychology and Health. ISSN 0887-0446. 27(1), p. 1–12. doi: 10.1080/08870446.2010.540665. Full text in Research Archive
• Vassend, Olav & Skrondal, Anders (2011). The NEO personality inventory revised (NEO-PI-R): Exploring the measurement structure and variants of the five-factor model. Personality and Individual Differences. ISSN 0191-8869. 50(8), p. 1300–1304. doi: 10.1016/j.paid.2011.03.002. Full text in Research Archive
• Vassend, Olav; Quale, Anette Johansen; Røise, Olav & Schanke, Anne-Kristine (2011). Predicting the long-term impact of acquired severe injuries on functional health status: The role of optimism, emotional distress, and pain. Spinal Cord. ISSN 1362-4393. 49(12), p. 1193–1197. doi: 10.1038/sc.2011.70. Full text in Research Archive
• Vassend, Olav; Røysamb, Espen & Nielsen, Christopher Sivert (2011). Dental anxiety in relation to neuroticism and pain sensitivity. A twin study. Journal of Anxiety Disorders. ISSN 0887-6185. 25(2), p. 302–308. doi: 10.1016/j.janxdis.2010.09.015. Full text in Research Archive
• Mohn, Christine; Vassend, Olav & Knardahl, Stein (2011). Psychophysiological responses to pain stimulation and cognitive tasks in female temporomandibular disorder patients. Scandinavian Journal of Pain. ISSN 1877-8860. 2(2), p. 72–82. doi: 10.1016/j.sjpain.2010.12.001. Full text in Research Archive Show summary

  Background and purpose Psychophysiological factors may contribute to the development of temporomandibular disorders (TMD). Both local orofacial and systemic responses have been investigated. However, most studies have concentrated on physiological responding during cognitive challenges, while responses during painful tasks may be highly relevant for the development of chronic pain conditions. Moreover, the relationship between experimental challenges and physiological responding may be influenced by affective responses during the experimental tasks, an issue not often considered in the literature. Methods This study compared electromyography (EMG) of the left masseter and left trapezius muscles, orofacial and digital skin blood-flow (SBF), mean arterial pressure (MAP), and heart rate (HR) at rest, during orofacial isometric contraction, electrocutaneous pain stimulation of the left hand, pressure pain stimulation of the masseter muscle and the sternum, and three cognitive tasks (reading aloud, a simulated job interview, and visuomotoric tracking). The participants were 25 TMD patients and 25 matched pain-free controls, all females. Affective responses were assessed with the State part of the State-Trait Personality Inventory and with Visual Analogue Scales. Results Masseter EMG levels were significantly lower in the TMD group relative to the control group during jaw contraction, pressure pain stimulation, the relaxation periods, and cognitive tasks. SBF, MAP, and HR responses were largely similar in the two groups, with SBF responses to pain stimulation evident at lower levels of stimulation than previously found. The TMD patients reported significantly higher levels of negative affect during the experiment. Conclusions and implications The low EMG responses in the TMD group may be taken in support of the Pain Adaptation Model of musculoskeletal pain, in which reduced muscular activity serves to protect a painful area. However, it may also be supportive of the Integrated Pain Adaptation Model, where higher central nervous structures influence local muscular output. The group similarities in systemic physiological responding in combination with the elevated levels of negative state affect in the TMD patients confirm previous reports of psychosocial differences being more reliable indicators of TMD than generalized physiological responding.

• Mohn, Christine; Vassend, Olav; Krogstad, Berit Heyerdahl & Knardahl, Stein (2010). Personality traits and subjective health complaints in female TMD patients and healthy controls. The Open Pain Journal. 3, p. 134–143. doi: 10.2174/1876386301003010134. Full text in Research Archive Show summary

  Abstract: Background: Personality traits and general health complaints may influence the course of and treatment of chronic pain. However, only few studies compare more than one or two personality characteristics in chronic pain patients and healthy controls. This study compares the comprehensive non-pathological personality structure of female patients with temporomandibular disorders (TMD) and pain-free controls. Moreover, this study controls for the influence of Neuroticism, self-presentation bias, and acute pain sensitivity on the subjective report of general health complaints. Methods: Twenty-five TMD patients were compared to 25 matched controls on personality traits (NEO Personality Inventory-Revised; NEO-PI-R), self-presentation bias (Social Desirability Scale; SDS), psychological distress (Symptom Checklist 90-Revised; SCL-90-R), and general somatic complaints. Experimental pain sensitivity was assessed by electrocutaneous and pressure pain stimulation. Results: Compared to the controls, Extraversion and Openness were lower in the TMD group, and the TMD patients exhibited higher levels of psychological and musculoskeletal complaints also when Neuroticism, self-presentation bias, and acute pain sensitivity were held constant. Conclusions: Low levels of Extraversion and Openness may dispose TMD patients to isolation and negative thought patterns. The elevated levels of psychological distress and general musculoskeletal pain in the TMD group add to previous reports of TMD as a complex condition also involving structures and processes outside of the orofacial region.

• Mohn, Christine; Vassend, Olav & Knardahl, Stein (2008). Experimental pain sensitivity in women with temporomandibular disorders and pain-free controls: the relationship to orofacial muscular contraction and cardiovascular responses. The Clinical Journal of Pain. ISSN 0749-8047. 24(4), p. 343–352. doi: 10.1097/AJP.0b013e318162eaf4. Full text in Research Archive Show summary

  OBJECTIVE: Chronic pain may result both from a generalized hypersensitivity to acute pain, suggestive of central sensitization processes, and dysfunction of the endogenous pain regulatory system. One purpose of this study was to compare experimental pain sensitivity at several anatomic sites in temporomandibular disorder (TMD) patients and pain-free controls during baseline and after standardized mechanical load of the orofacial region. A second purpose was to compare the pain-modulating effects of cardiovascular responses in TMD patients and pain-free controls. METHODS: Experimental pain was induced by electrocutaneous stimulation of the dorsal left hand and pressure algometry at the right masseter muscle and the sternum. The pain sensitivity of the orofacial region was manipulated by isometric contraction of the masseter muscles. Elevations of mean arterial pressure and heart rate were induced by a simulated job interview. RESULTS: At baseline, the TMD patients exhibited a significantly higher electrocutaneous pain threshold. Relative to the healthy controls, the TMD patients reported increased electrocutaneous and pressure pain sensitivity after isometric contraction of the orofacial region. In addition, there were correlations between mean arterial pressure and pain sensitivity in the TMD group only. DISCUSSION: Significant increases in generalized pain sensitivity occurred in the TMD group, but not in the control group, after isometric contraction of the orofacial muscles, suggestive of a central sensitization process in TMD. Moreover, only in the TMD group there were significant associations between cardiovascular responsesand pain sensitivity, challenging previous assumptions of this relationship occurring mainly in pain-free individuals.

• Nielsen, Christopher Sivert; Stubhaug, Audun; Price, Donald D; Vassend, Olav; Czajkowski, Nikolai & Harris, Jennifer (2008). Individual differences in pain sensitivity: Genetic and environmental contributions. Pain. ISSN 0304-3959. 136(1-2), p. 21–29. doi: 10.1016/j.pain.2007.06.008. Full text in Research Archive
• Vassend, Olav & Knardahl, Stein (2005). Effects of repeated electrocutaneous pain stimulation on facial blood flow. Biological Psychology. ISSN 0301-0511. 68(2), p. 163–178. doi: 10.1016/j.biopsycho.2004.04.004. Full text in Research Archive Show summary

  The purpose of the study was to examine the effects of repeated electrocutaneous pain stimulation of the hand on facial blood flow responses in healthy human subjects (58 adult women). Finger blood flow, mean arterial blood pressure, and heart rate were also monitored. To investigate the influence of psychological factors, the subjects’ affect states were assessed, and physiological responding was explored during cognitive distraction, i.e., when attention was turned away from the unpleasant stimulus. Consistently, electrocutaneous stimulation elicited vasodilatation in the cheek, together with finger vasoconstriction. This response pattern was evident even at non-painful stimulation intensities. The facial blood flow response showed habituation across stimulation trials and was largely unrelated to systemic cardiovascular changes, affect states, and attentional manipulation. These findings indicate (1) that the experimentally induced facial blood flow changes are part of a non-specific physiological response pattern elicited during noxious stimulation, and (2) that they are not dependent on regional (orofacial) stimulation for their occurrence.

• Nielsen, Christopher Sivert; Price, Donald D.; Vassend, Olav; Stubhaug, Audun & Harris, Jennifer R. (2005). Characterizing individual differences in heat-pain sensitivity. Pain. ISSN 0304-3959. 119(1-3), p. 65–74. Full text in Research Archive
• Vassend, Olav & Knardahl, Stein (2005). Personality, affective response, and facial blood flow during brief cognitive tasks. International Journal of Psychophysiology. ISSN 0167-8760. 55(3), p. 265–278. doi: 10.1016/j.ijpsycho.2004.08.005. Full text in Research Archive Show summary

  Blood pressure, heart rate, and changes in facial and finger blood flow were monitored in 58 women during three laboratory tasks, i.e., reading out a neutral text, a personally relevant speech (including a silent preparation phase), and a tracking task. Participants rated the tasks as mild to moderate with regard to affect intensity. Significant effects of personality on affect states were demonstrated, indicating higher levels of anxiety, depression, and anger in the high-neuroticism group, and more curiosity in the high-extraversion group. Arterial pressure, heart rate, and facial blood flow increased during task performance in all three conditions. No relationship between facial blood flow changes and muscle activity measured by m. masseter electromyography (EMG) were demonstrated. Digital vasoconstriction occurred in parallel with facial vasodilatation during tracking and in the preparation phase before the speech. There were no moderator effects of neuroticism or extraversion on blood flow or other cardiovascular responses.

• Watten, Reidulf G. & Vassend, Olav (2005). Personality and intelligence. In Faleide, Asbjørn O. (Eds.), Selvregulering, personlighet og helse : et psykofysiologisk og psykosomatisk perspektiv. Unipub forlag. ISSN 9788274772076. p. 143–159. Full text in Research Archive
• Vassend, Olav & Knardahl, Stein (2004). Cardiovascular responsiveness to brief cognitive challenges and pain sensitivity in women. European Journal of Pain. ISSN 1090-3801. 8(4), p. 315–324. doi: 10.1016/j.ejpain.2003.10.006. Full text in Research Archive
• Willumsen, Tiril & Vassend, Olav (2003). Effects of cognitive therapy, applied relaxation and nitrous oxide sedation. A five-year follow-up study of patients treated for dental fear. Acta Odontologica Scandinavica. ISSN 0001-6357. 61, p. 93–99. Full text in Research Archive
• Willumsen, Tiril; Vassend, Olav & Hoffart, Asle (2001). One-year Follow-up of Patients Treated for Dental Fear: Effects of Cognitive Therapy, Applied Relaxation and Nitrous Oxide Sedation. Acta Odontologica Scandinavica. ISSN 0001-6357. 59, p. 335–340. Full text in Research Archive Show summary

  Effects of dental fear treatments were assessed in a one-year follow-up study. Sixty-two patients had finished a controlled study in which they were randomly allocated to nitrous oxide sedation (NO), cognitive therapy (CT) or applied relaxation (AR). During the trial, highly significant reductions in dental fear and general distress were observed. One year after, a majority (95%) of the participants had attended dental treatment in general practice. On the whole, continued favourable effects with regard to dental fear and general distress were observed. Patients in the applied relaxation group evidenced the largest reductions on the dental fear measures. All patients judged the dental fear treatment to have been beneficial, and 80% judged the treatment given in the year after the dental fear treatment as successful. All three treatment groups scored in the normative range for general distress at the end of treatment as well as at follow-up.

• Willumsen, Tiril; Vassend, Olav & Hoffart, Asle (2001). A Comparison of Cognitive Therapy, Applied Relaxation and Nitrous Oxide Sedation in the Treatment of Dental Fear. Acta Odontologica Scandinavica. ISSN 0001-6357. 59, p. 290–296. Full text in Research Archive Show summary

  The aim of this study was to investigate the short-term efficacy of cognitive therapy and applied relaxation in dental fear treatment, and to compare these methods with conventional pharmacological sedation (nitrous oxide sedation). Patients (n=65) suffering from severe dental fear were randomly assigned to the different treatment methods and received 10 weekly sessions of individual therapy. Drop-out rates were low, and all patients who completed the therapy sessions were able to receive dental treatment. Scores on dental fear tests were significantly reduced compared to pre-treatment level for all treatment groups. There were no major differences between treatment methods in this short time perspective.

• Vassend, Olav; Willumsen, Tiril & Hoffart, Asle (2000). Effects of dental fear treatment on general distress. The role of personality variables and treatment method. Behavior Modification. ISSN 0145-4455. 24(4), p. 580–599. Full text in Research Archive
• Vassend, Olav & Skrondal, Anders (1999). The role of negative affectivity in self-assessment of Health. A structural equation approach. Journal of Health Psychology. ISSN 1359-1053. 4(4), p. 465–482. Full text in Research Archive
• Vassend, Olav & Skrondal, Anders (1999). The problem of structural indeterminacy in multidimensional symptom report instruments. The case of SCL-90-R. Behaviour Research and Therapy. ISSN 0005-7967. 37, p. 685–701. Full text in Research Archive
• Vassend, Olav & Eskild, Anne (1998). Psychological distress, coping, and disease progression in HIV-positive homosexual men. Journal of Health Psychology. ISSN 1359-1053. 3(2), p. 243–257. Full text in Research Archive Show summary

  The objectives of the study were (1) to examine the role of coping styles in disease progression in models controlling for initial CD4+ cell counts, distress, and health behavior in a sample of HIV positive homosexual men (n = 65), and (2) to investigate the relationship between coping styles and distress (e.g. depression, anxiety, negative ruminations). A consistent association between planful problem-solving coping and disease progression was demonstrated. Distress was positively correlated with indicators of passive-defensive coping style (e.g. self-controlling, escape-avoidance), and negatively correlated with planful problem-solving and positive reappraisal. The results suggest that coping styles may merit a specific focus in future research of psychological factors in HIV infection, particularly as they may relate to both medical outcome and social/emotional aspects of being HIV infected.

• Watten, Reidulf G.; Vassend, Olav; Myhrer, Trond & Syversen, Jon-Lars (1997). Personality factors and somatic symptoms. European Journal of Personality. ISSN 0890-2070. 11, p. 57–68. Full text in Research Archive
• Vassend, Olav & Skrondal, Anders (1997). Validation of the NEO Personality Inventory and the five-factor model. Can findings from exploratory and confirmatory factor analysis be reconciled? European Journal of Personality. ISSN 0890-2070. 11, p. 147–166. Full text in Research Archive
• Vassend, Olav; Eskild, Anne & Halvorsen, Ragnhild (1997). Negative affectivity, coping, immune status, and disease progression in HIV infected individuals. Psychology and Health. ISSN 0887-0446. 12, p. 375–388. Full text in Research Archive
• Krogstad, Berit Schie; Jokstad, Asbjørn; Dahl, Bjørn L. & Vassend, Olav (1996). Relationships between risk factors and treatment outcome in a group of patients with Temporomandibular disorders. Journal of Orofacial Pain. ISSN 1064-6655. 10, p. 48–53. Full text in Research Archive
• Krogstad, Berit Schie; Jokstad, Asbjørn; Dahl, Bjørn L. & Vassend, Olav (1996). The reporting of pain, somatic complaints, and anxiety in a group of TMD-patients before and after two years treatment. Sex differences. Journal of Orofacial Pain. ISSN 1064-6655. 10, p. 263–269. Full text in Research Archive
• Watten, Reidulf G.; Vassend, Olav; Syversen, Jon-Lars & Myhrer, Trond (1995). Personality and quality of life. Social Indicators Research. ISSN 0303-8300. 35, p. 289–302. Full text in Research Archive
• Vassend, Olav & Skrondal, Anders (1995). Factor analytic studies of the NEO Personality Inventory and the five-factor model: The problem of high structural complexity and conceptual indeterminacy. Personality and Individual Differences. ISSN 0191-8869. 19, p. 135–147. Full text in Research Archive
• Vassend, Olav; Krogstad, Berit Schie & Dahl, Bjørn (1995). Negative affectivity, somatic complaints, and symptoms of temporomandibular disorders. Journal of Psychosomatic Research. ISSN 0022-3999. 39, p. 889–899. Full text in Research Archive
• Wisløff, T.F.; Vassend, Olav & Asmyhr, Ø. (1995). Dental anxiety, utilization of dental services, and DMFS status in Norwegian military recruits. Community Dental Health. ISSN 0265-539X. 12, p. 100–103. Full text in Research Archive
• Vassend, Olav (1994). Negative affectivity, subjective somatic complaints, and objective health indicators. Mind and body still separated? In Maes, Stan; Leventhal, Harold & Johnston, Marie (Ed.), International Review of Health Psychology, Volume 3. John Wiley & Sons. ISSN 9780471944560. p. 97–118. Full text in Research Archive
• Vassend, Olav; Watten, Reidulf G.; Myhrer, Trond & Syvertsen, Jon Lars (1994). Negative affectivity and intellectual ability: A study of their relation to self-reported physical symptoms, perceived daily stress and mood, and disciplinary problems in military recruits. Social Science and Medicine. ISSN 0277-9536. 39(4), p. 583–590. Full text in Research Archive
• Vassend, Olav (1993). Anxiety, pain and discomfort associated with dental treatment. Behaviour Research and Therapy. ISSN 0005-7967. 31, p. 659–666. Full text in Research Archive
• Lian, Lilleba; Vassend, Olav Mandt & Andersen, Harald T. (1993). Norske versjoner av NEO-Personality Inventory, Symptom Checklist 90 Revised og Giessen Subjective Complaints List. Del II. Tidsskrift for Norsk psykologforening (Psykologtidsskriftet). ISSN 0332-6470. 30, p. 117–126. Full text in Research Archive
• Vassend, Olav Mandt; Lian, Lilleba & Andersen, Harald T. (1992). Norske versjoner av NEO-Personality Inventory, Symptom Checklist 90 Revised og Giessen Subjective Complaints List. Del I. Tidsskrift for Norsk psykologforening (Psykologtidsskriftet). ISSN 0332-6470. 29(29), p. 1150–1160. Full text in Research Archive
• Grytten, Jostein Ivar; Holst, Dorthe; Rossow, Ingeborg; Vassend, Olav & Wang, Nina J. (1990). Nytt om befolkningens tenner og tannhelse. Den norske tannlegeforenings Tidende. ISSN 0029-2303. 100, p. 414–422. Full text in Research Archive
• Vassend, Olav (1989). Dimensions of negative affectivity, self-reported somatic symptoms, and health-related behaviors. Social Science and Medicine. ISSN 0277-9536. 28, p. 29–36. Full text in Research Archive
• Vassend, Olav (1989). Hypnotizability, imaginative involvement, and anxiety. Scandinavian Journal of Psychology. ISSN 0036-5564. 30, p. 30–36. Full text in Research Archive
• Vassend, Olav (1988). Dimensions of hypnotic Depth: An exploratory study. Scandinavian Journal of Psychology. ISSN 0036-5564. 29, p. 207–213. Full text in Research Archive
• Vassend, Olav (1987). Personality, imaginative involvement, and self-reported somatic complaints. Relevance to the concept of alxithymia. Psychotherapy and Psychosomatics. ISSN 0033-3190. 47, p. 74–81. Full text in Research Archive
• Vassend, Olav (1987). Examination stress, personality, and self-reported physical symptoms. Scandinavian Journal of Psychology. ISSN 0036-5564. 29, p. 21–32. Full text in Research Archive
• Halvorsen, Ragnhild & Vassend, Olav (1987). Effects of examination stress on some cellular immunity functions. Journal of Psychosomatic Research. ISSN 0022-3999. 31, p. 693–701. Full text in Research Archive
• Vassend, Olav; Halvorsen, Ragnhild & Norman, Nils (1987). Hormonal and psychological effects of examination stress. Scandinavian Journal of Psychology. ISSN 0036-5564. 28, p. 75–82. Full text in Research Archive
• Vassend, Olav & Halvorsen, Ragnhild (1987). Personality, examination stress and serum concentrations of immunoglobulins. Scandinavian Journal of Psychology. ISSN 0036-5564. 28, p. 233–241. Full text in Research Archive
• Vassend, Olav Mandt (1986). Psykoimmunologi: Teorier og forskning. Tidsskrift for Norsk psykologforening (Psykologtidsskriftet). ISSN 0332-6470. 23, p. 221–233. Full text in Research Archive
• Vassend, Olav (1985). Begreper og teoridannelse i psykosomatisk forskning. Noen utvalgte emner. Del II. Tidsskrift for Norsk psykologforening (Psykologtidsskriftet). ISSN 0332-6470. 22, p. 613–626. Full text in Research Archive
• Vassend, Olav (1985). Begreper og teoridannelse i psykosomatisk forskning. Noen utvalgte emner. Del I. Tidsskrift for Norsk psykologforening (Psykologtidsskriftet). ISSN 0332-6470. 22, p. 549–560. Full text in Research Archive
• Vassend, Olav (1985). Somatiske og psykologiske aspekter ved asthma bronchiale hos barn. Nordisk Psykiatrisk Tidsskrift. ISSN 0029-1455. 39, p. 493–500. Full text in Research Archive
• Vassend, Olav (1985). Hypnose og psykoanalytisk orientert terapi. Noen generelle problemer og prinsipper. Nordisk Psykiatrisk Tidsskrift. ISSN 0029-1455. 39, p. 29–36. Full text in Research Archive
• Vassend, Olav (1985). Psykosomatikkbegrepet. Forsøk på en avgrensning. Agrippa - psykiatriske tekster. ISSN 0106-0457. 4, p. 251–262. Full text in Research Archive
• Vassend, Olav (1984). Paradoksal familieterapi. Teori, prinsipper og teknikker. Fokus på familien/ Nordisk tidsskrift for familie- og relasjonsarbeid. ISSN 0332-5415. 12, p. 67–85. Full text in Research Archive
• Vassend, Olav (1984). Sykdom, familie og mestring. Fokus på familien/ Nordisk tidsskrift for familie- og relasjonsarbeid. ISSN 0332-5415. 12, p. 187–201. Full text in Research Archive
• Vassend, Olav; Bjærke, Stian & Faleide, Asbjørn O. (1983). Familieinteraksjon og astma hos barn. En undersøkelse med Familie-Rorschach. Fokus på familien/ Nordisk tidsskrift for familie- og relasjonsarbeid. ISSN 0332-5415. 3, p. 123–134. Full text in Research Archive
• Vassend, Olav (1983). Det ubevisste og selv-innsikt. En filosofisk undersøkelse. Agrippa - psykiatriske tekster. ISSN 0106-0457. 5, p. 261–281. Full text in Research Archive
• Vassend, Olav (1983). Psykologiske metoder ved behandling av pasienter med asthma bronchiale. En litteraturoversikt. Tidsskrift for Norsk psykologforening (Psykologtidsskriftet). ISSN 0332-6470. 20, p. 520–531. Full text in Research Archive
• Vassend, Olav (1983). Barn med astma. En studie av foreldre-barn kommunikasjon i en konfliktsituasjon. Fokus på familien/ Nordisk tidsskrift for familie- og relasjonsarbeid. ISSN 0332-5415. 3, p. 95–111. Full text in Research Archive
• Vassend, Olav (1981). Psykososiale faktorer ved asthma bronchiale hos barn: Teorier og forskning. Fokus på familien/ Nordisk tidsskrift for familie- og relasjonsarbeid. ISSN 0332-5415. 2. Full text in Research Archive

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• Vassend, Olav (1997). Kommunikasjon og pasientbehandling. Praktisk psykologi for helsepersonell med eksempler fra odontologi. Spartacus. ISBN 9788243000582. 239 p. Full text in Research Archive
• Vassend, Olav & Skrondal, Anders (1996). A study of the NEO personality inventory and the five factor model. Factor models and descriptive statistics based on a Norwegian national sample. Norsk Psykologforening. ISBN 9788291473048. -1 p. Full text in Research Archive

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• 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
• Eftedal, Nikolai Haahjem; Kleppestø, Thomas Haarklau; Røysamb, Espen; Vassend, Olav; Ystrøm, Eivind & Thomsen, Lotte (2019). Moral opportunism: A unique genetic grounding associates lesser guilt from perpetrating injustice with greater sensitivity to being the victim of it. Full text in Research Archive
• Kleppestø, Thomas Haarklau; Czajkowski, Nikolai Olavi; Vassend, Olav; Røysamb, Espen; Eftedal, Nikolai Haahjem & Kunst, Jonas R. [Show all 8 contributors for this article] (2019). Social dominance orientation has both genetic and unique environmental influences, but only genetic pleiotropy accounts for its correlation with political attitudes. Full text in Research Archive
• Røysamb, Espen; Nes, Ragnhild Bang; Czajkowski, Nikolai Olavi & Vassend, Olav (2017). Anxiety, depression and life satisfaction after midlife. A twin study across 20 years. Full text in Research Archive
• Nes, Ragnhild Bang; Czajkowski, Nikolai Olavi; Røysamb, Espen & Vassend, Olav (2017). Components and sources of well-being and ill-being: A twin study. Full text in Research Archive
• Vassend, Olav; Nielsen, Christopher Sivert; Røysamb, Espen & Czajkowski, Nikolai Olavi (2017). Fatigue symptoms in relation to neuroticism, anxiety-depression, and musculoskeletal pain. A longitudinal study. Full text in Research Archive
• Kleppestø, Thomas H.; Czajkowski, Nikolai Olavi; Vassend, Olav; Røysamb, Espen; Kunst, Jonas R. & Thomsen, Lotte (2017). Preferring domination or egalitarianism: Genetic and environmental structure of Social Dominance Orientation. Full text in Research Archive
• Czajkowski, Nikolai Olavi; Nes, Ragnhild Bang; Vassend, Olav & Røysamb, Espen (2017). Effects of somatic and mental illness on subjective well-being. A discordant twin analysis. Full text in Research Archive
• Mohn, Christine; Vassend, Olav & Knardahl, Stein (2002). Effects of distraction on experimental pain in temporomandibular disorders (TMD) and healthy controls. Full text in Research Archive
• Mohn, Hanne Christine; Vassend, Olav & Knardahl, Stein (2002). Personality traits and psychological distress in temporomandibular disorders (TMD). Full text in Research Archive
• Reinvang, Ivar; Vassend, Olav & Middelborg, Jon (1996). ERP indicators of processing of semantic distractors in normal subjects. Psychophysiology. ISSN 0048-5772. 32, p. 62–62. Full text in Research Archive
• Holst, Dorthe; Grytten, Jostein Ivar; Rossow, Ingeborg; Wang, Nina Johanne & Vassend, Olav (1990). Loss of teeth in the adult population in Norway. Full text in Research Archive
• Vassend, Olav (2005). Cardiovascular responsiveness to pain stimulation and brief cognitive challenges. Relationship to pain sensitivity. (Thesis for the Degree of Cand. Scient.). Institutt for molekylær biovitenskap. Full text in Research Archive
• Vassend, Olav & Skrondal, Anders (2003). Interpretation of the SCL-90-R. A psychometric study based on a Norwegian national sample. Institutt for flymedisin. ISSN 9788292487013. Full text in Research Archive
• Vassend, Olav (1988). Examination stress, personality, and somatic responses. Universitetet i Oslo. ISSN 9788256909360. Full text in Research Archive

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