Svenn Torgersen

• Torgersen, Svenn Omar; Skaug, Eirunn & Waaktaar, Trine (2026). Common and Unique Etiological Influences on Personality and Personality Disorders in Youth. Psychopathology. ISSN 0254-4962. doi: 10.1159/psp/aelag006. Full text in Research Archive Show summary

  Background: Personality and personality disorders (PDs) are closely related constructs, but the nature of their relationship remains uncertain. Dimensional models suggest PDs are extreme manifestations of personality traits. We investigated the etiological links between broad personality factors and dimensional PD factors using quantitative analyses of common and unique genetic and environmental etiological factors affecting both normative and deviant personalities, emphasizing methods to minimize measurement bias. Methods: Seven national twin cohorts participated (N = 2,353 twins from 1,188 families), assessing personality traits with questionnaires across three adolescent waves and PD traits via age-19 clinical interviews. Exploratory factor analyses of personality traits and the three-cluster ABC factors of PDs simplified the factor structure of the measures. Biometric twin analyses with Cholesky modeling identified genetic and environmental links among factors. Results: Factor analysis of personality traits yielded non-resilient, disinhibited, and disaffected factors. PDs fit an emotional/erratic, anxious/fearful, and odd/eccentric factor structure. Phenotypic correlations varied, but the disinhibited factor had minimal relations to specific PD factors. Crucially, approximately one-third of the genetic variance was shared between personality and PDs. However, the majority of genetic variance and all non-shared environmental variance were trait-specific, suggesting predominantly distinct etiological pathways. Conclusion: The significant genetic overlap supports the continuum model; results were bolstered by using broad factors and method triangulation. However, unique genetic and environmental influences point to distinct etiological pathways differentiating personality and PDs. These findings endorse the continuum model yet highlight the need for further research to grasp the complex relationships between personality and PDs.

• Skaug, Eirunn; Waaktaar, Trine & Torgersen, Svenn Omar (2026). Stability and Change in Wellbeing Throughout Adolescence and Its Relationship with Life Events: A Longitudinal Twin Study. Behavior Genetics. ISSN 0001-8244. doi: 10.1007/s10519-026-10262-4. Full text in Research Archive
• Waaktaar, Trine; Skaug, Eirunn & Torgersen, Svenn Omar (2025). The etiological relationship between the general factors of psychopathology and personality; a longitudinal twin study from adolescence into young adulthood. Frontiers in Psychology. 16. doi: 10.3389/fpsyg.2025.1564305. Full text in Research Archive Show summary

  Background: Mental disorders and normal personality are interconnected domains. Recent studies highlight the dimensional and hierarchical nature of psychopathology and personality, focusing on their general factor levels. However, their relationship remains unclear. Aims: This study explored the etiological relationship between the general factors of psychopathology and personality from adolescence to young adulthood. Methods: Longitudinal data from seven national twin cohorts (N = 1,538 pairs) were collected across three waves (ages 12–22). Data was analyzed using a genetically informative random intercept cross-lagged panel model and Cholesky decomposition modeling. Results: Negligible cross-lagged effects were observed between the general factors. Both showed substantial stability, with genetic influences explaining most of the time-invariant variance. About one-quarter of genetic stability was shared. Conclusion: Psychopathology and personality are distinct yet parallel domains developing through adolescence into young adulthood. Notably, change in one did not lead to change in the other.

• Skaug, Eirunn; Waaktaar, Trine & Torgersen, Svenn Omar (2024). The relationship between personality throughout adolescence and social anxiety disorder in young adulthood. A longitudinal twin study. PLOS ONE. 19(3). doi: 10.1371/journal.pone.0299766. Full text in Research Archive Show summary

  This study examined the longitudinal relationship between a range of personality related variables measured throughout adolescence, and social anxiety disorder (SAD) in young adulthood. In addition, we examined to what degree the phenotypic associations between personality and SAD could be attributed to shared genetic and environmental factors, respectively. A total of 3394 twins (56% females), consisting of seven national birth cohorts from Norway, participated in the study. Personality was measured with self-report questionnaires at three times throughout adolescence, and SAD was measured with a diagnostic interview in early adulthood (M = 19.1 years, SD = 1.2). Correlation and regression analyses were performed to examine phenotypic associations between personality and SAD. We then created four composite scores of personality, in which the personality variables from four different ages throughout adolescence were weighted relative to their importance for SAD. Finally, a series of Cholesky decomposition models were used to examine the underlying genetic and environmental influences on the phenotypic associations between composite scores of personality and SAD. The results showed that especially higher neuroticism, lower extraversion, higher levels of loneliness, and lower levels of resilience, self-efficacy and sense of coherence, were associated with SAD. The phenotypic correlations between composite scores of personality and SAD increased from 0.42 when personality was measured 6–7 years prior to the assessment of SAD, to 0.52 when personality was measured shortly before the assessment of SAD. These phenotypic associations were mainly due to genetic influences, indicating that personality in adolescence predicts SAD in early adulthood due to shared genetic influences rather than having direct ‘causal’ effects on SAD.

• 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.

• Vollrath, Margarete E.; Eilertsen, Espen Moen; Torgersen, Svenn Omar; Gjerde, Line Cecilie & Ystrøm, Eivind (2024). Bridging Temperament and the Big Five in Children: A Genetically Informative Study. Journal of Personality and Social Psychology. ISSN 0022-3514. 126(4), p. 660–675. doi: 10.1037/pspp0000500. Full text in Research Archive Show summary

  Early temperament precedes children’s emerging Big Five personality, but shared models of temperament and personality are scarce. We wanted to estimate the genetic factor structure underlying both temperament and the Big Five in children, employing a genetically informed study. Within the Norwegian Mother and Child Cohort Study, we selected 26,354 twins, siblings, and cousins. Mothers rated their children’s temperament three times between the ages of 1.5 and 5 years, and the children’s Big Five personality at the age of 8. We analyzed the data using biometric modeling. The mean heritability of single-time temperamental traits and Big Five personality traits was .48 and .45, respectively. The mean genetic correlations of temperament across time were .80. The genetic correlations of temperament at 5 years and the Big Five at 8 years revealed two factors, the first comprising reversed Big Five Neuroticism, Agreeableness, Conscientiousness, and reversed EAS Emotionality, the second comprising Big Five Extraversion, Openness to Experience, EAS Activity, Sociability, and reversed Shyness. A confirmatory factor analysis estimated the two factors showing heritabilities of .96 and .72, respectively. The two factors mirrored the metatraits Stability and Plasticity by John M. Digman. Temperament and personality in childhood can be meaningfully bridged using just two metafactors.

• Jørstad, Marie Lindvik; Scarth, Morgan; Torgersen, Svenn Omar; Pope, Harrison Graham & Bjørnebekk, Astrid Kristine (2023). Clustering psychopathology in male anabolic–androgenic steroid users and nonusing weightlifters. Brain and Behavior. doi: 10.1002/brb3.3040. Full text in Research Archive
• 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.

• Scarth, Morgan; Jørstad, Marie Lindvik; Reierstad, Amund; Klonteig, Sandra; Torgersen, Svenn & Hullstein, Ingunn Riise [Show all 7 contributors for this article] (2022). Psychopathology among anabolic-androgenic steroid using and non-using female athletes in Norway. Journal of Psychiatric Research. ISSN 0022-3956. 155, p. 295–301. doi: 10.1016/j.jpsychires.2022.09.023. Full text in Research Archive Show summary

  Anabolic-androgenic steroids (AAS) are primarily used to improve physical appearance and increase lean muscle mass. Due to their masculinizing properties, the majority of people using AAS are men; however, AAS use among females may increase with changing body ideals trending towards a more muscular appearance. AAS use among males have been associated with risk-taking behavior, and increased prevalence of personality disorders and psychopathology. As a result of low perceived prevalence and stigma among females who use AAS, the relationship between AAS use and psychopathology in this population is not well-known. AAS using women (n = 16) and weight-lifting controls (WLC) (n = 16) completed questionnaires regarding AAS use, health and training information. Psychopathology was evaluated using the Millon Clinical Multiaxial Inventory-III (MCMI-III). Group differences on demographic variables and scores on MCMI-III scales were evaluated with Mann-Whitney U tests. The clinical cut-off was then applied to all MCMI-III scales and groups were compared using Fisher's exact test. AAS consumers demonstrated significantly greater psychopathology than WLC on several scales. Externalizing personality disorder scales were elevated among those who use AAS relative to controls, such as borderline (p < 0.001), antisocial (p = 0.007) and sadistic (p = 0.002), and in addition depressive (p = 0.012), negativistic (p = 0.001) and masochistic (p = 0.029) personality disorders scales. Furthermore, all clinical syndromes were elevated among AAS consumers. AAS consumers thus demonstrated multi-pathology, and 56% (n = 9) of the group met the clinical criteria for six or more disorders. Females who use AAS experience in general increased levels of psychopathology compared to WLC. Clinicians should be aware of these traits and the challenges they present in providing care to this population.

• 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.

• Scarth, Morgan; Havnes, Ingrid Amalia; Jørstad, Marie Lindvik; McVeigh, Jim; Hout, Marie Claire Van & Westlye, Lars Tjelta [Show all 8 contributors for this article] (2022). Severity of anabolic steroid dependence, executive function, and personality traits in substance use disorder patients in Norway. Drug and Alcohol Dependence. ISSN 0376-8716. 231. doi: 10.1016/j.drugalcdep.2022.109275. Full text in Research Archive Show summary

  Introduction Anabolic androgenic steroids (AAS), including testosterone and synthetic derivatives, are typically used to increase muscle mass. Many users develop a dependence on these substances, contributing to worsened physical and mental health outcomes. Aspects of personality and executive dysfunction may represent underlying vulnerabilities for developing dependence. Objective To identify levels of AAS dependence within substance use disorder (SUD) treatment patients and assess the relationship between dependence severity and personality traits and executive function (EF). Methods Data were collected from patients at 38 SUD treatment facilities in Norway. Questionnaires were completed for measures of personality and EF. Measures of symptoms of AAS dependence were used in latent class analysis to identify sub-groups of patients, which were evaluated for association with EF and personality traits, and compared with a group of non-AAS using SUD patients. Results Three classes were identified; largely reflecting low, moderate, and high symptoms of dependence. Multinomial regression analyses indicated that moderate and high symptoms were associated with several measures of EF and personality traits, particularly self-monitoring, antagonism, disinhibition, and rigid perfectionism while users with low symptoms exhibited higher capacities for emotional control and shift, and lower negative affectivity, relative to non-AAS using SUD patients. Backward stepwise regressions indicated antagonism, and decreased self-monitoring as key personality and cognitive characteristics of SUD patients with severe AAS dependence. Conclusion Our findings indicate that specific executive dysfunctions and personality features, particularly those associated with poor emotional control, reduced empathy, and impulsivity are associated with more severe AAS dependence in the SUD population.

• Kandler, Christian; Waaktaar, Trine; Möttus, Rene; Riemann, Rainer & Torgersen, Svenn (2019). Unravelling the Interplay Between Genetic and Environmental Contributions in the Unfolding of Personality Differences from Early Adolescence to Young Adulthood. European Journal of Personality. ISSN 0890-2070. 33(3), p. 221–244. doi: 10.1002/per.2189. Full text in Research Archive Show summary

  In two studies, we examined the genetic and environmental sources of the unfolding of personality trait differences from childhood to emerging adulthood. Using self-reports from over 3000 representative German twin pairs of three birth cohorts, we could replicate previous findings on the primary role of genetic sources accounting for the unfolding of inter-individual differences in personality traits and stabilizing trait differences during adolescence. More specifically, the genetic variance increased between early (ages 10–12 years) and late (ages 16–18 years) adolescence and stabilized between late adolescence and young adulthood (ages 21–25 years). This trend could be confirmed in a second three-wave longitudinal study of adolescents’ personality self-reports and parent ratings from about 1400 Norwegian twin families (average ages between 15 and 20 years). Moreover, the longitudinal study provided evidence for increasing genetic differences being primarily due to accumulation of novel genetic influences instead of an amplification of initial genetic variation. This is in line with cumulative interaction effects between twins’ correlated genetic makeups and environmental circumstances shared by adolescent twins reared together. In other words, nature × nurture interactions rather than transactions can account for increases in genetic variance and thus personality variance during adolescence. © 2019 European Association of Personality Psychology

• Waszczuk, Monika Aldona; Waaktaar, Trine; Eley, Thalia C. & Torgersen, Svenn (2019). Etiological influences on continuity and co‐occurrence of eating disorders symptoms across adolescence and emerging adulthood. International Journal of Eating Disorders. ISSN 0276-3478. p. 1–10. doi: 10.1002/eat.23040. Full text in Research Archive Show summary

  Objective: The role of common and symptom‐specific genetic and environmental influences in maintaining eating disorder symptoms across development remains unclear. This study investigates the continuity and change of etiological influences on drive for thinness, bulimia, and body dissatisfaction symptoms and their co‐occurrence, across adolescence and emerging adulthood. Method: In total, 2,629 adolescent twins (mean age = 15.20, SD = 1.95) reported eating disorders symptoms across three waves of data collection. Biometric common pathways model was fitted to estimate genetic and environmental contributions to the continuity of each symptom over time, as well as time‐ and symptom‐specific influences. Results: Drive for thinness and body dissatisfaction symptoms showed a pattern of high continuity across development and high correlations with each other, whereas bulimia symptoms were moderately stable and less associated with the other two symptoms. Latent factors reflecting continuity of each symptom were largely under genetic influence (Al = 0.60–0.82). New genetic influences contributing to change in the developmental course of symptoms were observed in emerging adulthood. Genetic influences correlated considerably between the three symptoms. Non‐shared environmental influences were largely time‐and symptom‐specific, but some contributed moderately to the continuity across development (El = 0.18–0.40). The etiological overlap was larger between drive for thinness and body dissatisfaction symptoms than with bulimia symptoms. Discussion: The results provide preliminary evidence that stable as well as newly emerging genetic influences contribute to the co‐occurrence of drive for thinness, bulimia, and body dissatisfaction symptoms across adolescence and emerging adulthood. Conversely, environmental influences were less stable and contributed to change in symptoms over time.

• Torgersen, Svenn & Waaktaar, Trine (2019). The Oslo University Adolescent and Young Adult Twin Project: Recruitment and Attrition. Twin Research and Human Genetics. ISSN 1832-4274. p. 1–6. doi: 10.1017/thg.2019.51. Full text in Research Archive
• Waaktaar, Trine; Kan, Kees-Jan & Torgersen, Svenn (2018). The genetic and environmental architecture of substance use development from early adolescence into young adulthood: a longitudinal twin study of comorbidity of alcohol, tobacco and illicit drug use. Addiction. ISSN 0965-2140. 113(4), p. 740–748. doi: 10.1111/add.14076. Full text in Research Archive Show summary

  This is the peer reviewed version of the following article: Waaktaar, T., Kan, K.-J., and Torgersen, S. (2017) The genetic and environmental architecture of substance use development from early adolescence into young adulthood: a longitudinal twin study of comorbidity of alcohol, tobacco and illicit drug use. Addiction, which has been published in final form at http://dx.doi.org/10.1111/add.14076. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving."

• Øvergaard, Kristin Romvig; Ørbeck, Beate; Aase, Heidi; Torgersen, Svenn; Reichborn-Kjennerud, Ted & Zeiner, Pål (2018). Emotional Lability in Preschoolers With Symptoms of ADHD. Journal of Attention Disorders. ISSN 1087-0547. 22(8), p. 787–795. doi: 10.1177/1087054715576342. Full text in Research Archive Show summary

  OBJECTIVE: The aim of this study was to examine occurrence of emotional lability (EL) in preschoolers with ADHD symptoms versus controls. METHOD: The study was part of the Norwegian Mother and Child Cohort Study (MoBa) at the Norwegian Institute of Public Health. In the present study, 495 preschoolers were clinically examined. Symptoms of ADHD, anxiety, and oppositional defiant disorder (ODD) were measured with the Preschool Age Psychiatric Assessment Interview. An EL measure was obtained from the Emotional Control subscale of the Behavior Rating Inventory of Executive Function-Preschool Version (BRIEF-P), which parents and teachers completed. RESULTS: EL was significantly more frequent in the ADHD group compared with controls (25% vs. 7%, p < .001). By parent report, EL correlated significantly with ADHD-, anxiety-, and ODD symptoms. By teacher report, EL was significantly correlated only with hyperactivity-impulsivity. CONCLUSION: EL appears identifiable in young preschoolers and was particularly associated with ODD in children with ADHD symptoms.

• Vollrath, Margarete E.; Torgersen, Svenn & Torgersen, Leila (2018). Associations of children’s Big Five personality with eating behaviors. BMC Research Notes. 11(1). doi: 10.1186/s13104-018-3768-9. Full text in Research Archive Show summary

  Objective Our aim is to examine the associations of the Big Five personality factors with eating behaviors in children using a cross-sectional study in 1543 randomly Norwegian 7–12 year olds. Results Mothers rated the hierarchical personality inventory for children, and the child eating behaviour questionnaire to describe her child. Personality and eating behaviors were substantially associated in bivariate correlations and multivariate analyses of variance. The strongest predictors of eating behaviors were neuroticism, followed by agreeableness and conscientiousness. Neuroticism correlated the highest with slow eating, emotional undereating, food responsiveness, and emotional overeating, and showed minor associations with satiety responsiveness, and fussiness. Neuroticism was not associated with enjoyment of food. Agreeableness was associated with low fussiness, low emotional undereating, low food responsiveness and low emotional overeating, conscientiousness was associated with low satiety responsiveness, and food responsiveness, and extraversion and imagination were associated with high enjoyment of food.

• Gunderson, John G; Herpertz, Sabine; Skodol, Andrew E; Torgersen, Svenn & Zanarini, Mary C (2018). Borderline personality disorder. Nature Reviews Disease Primers. 4, p. 1–20. doi: 10.1038/nrdp.2018.29. Full text in Research Archive
• Christensen, Tore Buer; Paap, Muirne C. S.; Arnesen, Marianne; Koritzinsky, Karoline H.; Nysæter, Tor Erik & Eikenæs, Ingeborg Helene [Show all 14 contributors for this article] (2018). Interrater reliability of the structured clinical interview for the DSM-5 alternative model of personality disorders module i: Level of personality functioning scale. Journal of Personality Assessment. ISSN 0022-3891. 100(6), p. 630–641. doi: 10.1080/00223891.2018.1483377. Full text in Research Archive Show summary

  The fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM–5) presents an alternative model for personality disorders in which severity of personality pathology is evaluated by the Level of Personality Functioning Scale (LPFS). The Structured Interview for the DSM–5 Alternative Model for Personality Disorders, Module I (SCID–5–AMPD I) is a new tool for LPFS assessment, but its interrater reliability (IRR) has not yet been tested. Here we examined the reliability of the Norwegian translation of the SCID–5–AMPD I, applying two different designs: IRR assessment based on ratings of 17 video-recorded SCID–5–AMPD I interviews by five raters; and test–retest IRR based on interviews of 33 patients administered by two different raters within a short interval. For the video-based investigation, intraclass correlation coefficient (ICC) values ranged from .77 to .94 for subdomains, .89 to .95 for domains, and .96 for total LPFS. For the test–retest investigation, ICC ranged from .24 to .72 for subdomains, .59 to .90 for domains, and .75 for total LPFS. The test–retest study revealed questionable reliability estimates for some subdomains. However, overall the level of personality functioning was measured with a sufficient degree of IRR when assessed by the SCID–5–AMPD I.

• Korsgaard, Hans Ole; Torgersen, Svenn; Wentzel-Larsen, Tore & Ulberg, Randi (2016). Substance abuse and personality disorder comorbidity in adolescent outpatients: are girls more severely ill than boys? Child and Adolescent Psychiatry and Mental Health (CAPMH). 10:8(8), p. 1–9. doi: 10.1186/s13034-016-0096-5. Full text in Research Archive Show summary

  Background Substance use disorders (SUDs) constitute a major health problem and are associated with an extensive psychiatric comorbidity. Personality disorders (PDs) and SUDs commonly co-occur. Comorbid PD is characterized by more severe addiction problems and by an unfavorable clinical outcome. The present study investigated the prevalence of SUDs, PDs and common Axis I disorders in a sample of adolescent outpatients. We also investigated the association between PDs and SUDs, and how this association was influenced by adjustment for other Axis I disorders, age and gender. Methods The sample consisted of 153 adolescents, aged 14–17 years, who were referred to a non-specialized mental health outpatient clinic with a defined catchment area. SUDs and other Axis I conditions were assessed using the mini international neuropsychiatric interview. PDs were assessed using the structured interview for DSM-IV personality. Results 18.3 % of the adolescents screened positive for a SUD, with no significant gender difference. There was a highly significant association between number of PD symptoms and having one or more SUDs; this relationship was practically unchanged by adjustment for gender, age and presence of Axis I disorders. For boys, no significant associations between SUDs and specific PDs, conduct disorder (CD) or attention deficit hyperactivity disorder (ADHD) were found. For girls, there were significant associations between SUD and BPD, negativistic PD, more than one PD, CD and ADHD. Conclusions We found no significant gender difference in the prevalence of SUD in a sample of adolescents referred to a general mental health outpatient clinic. The association between number of PD symptoms and having one or more SUDs was practically unchanged by adjustment for gender, age and presence of one or more Axis I disorders, which suggested that having an increased number of PD symptoms in itself may constitute a risk factor for developing SUDs in adolescence. The association in girls between SUDs and PDs, CD and ADHD raises the question if adolescent girls suffering from these conditions may be especially at risk for developing SUDs. In clinical settings, they should therefore be monitored with particular diligence with regard to their use of psychoactive substances.

• Øvergaard, Kristin Romvig; Aase, Heidi; Torgersen, Svenn & Zeiner, Pål (2016). Co-Occurrence of ADHD and Anxiety in Preschool Children. Journal of Attention Disorders. ISSN 1087-0547. 20(7), p. 573–580. doi: 10.1177/1087054712463063. Full text in Research Archive
• Vollrath, Margarete E.; Hampson, Sarah E. & Torgersen, Svenn (2016). Constructing a short form of the hierarchical personality inventory for children (HiPIC): The HiPIC-30. Personality and Mental Health. ISSN 1932-8621. 10(2), p. 152–165. doi: 10.1002/pmh.1334. Full text in Research Archive
• Korsgaard, Hans Ole; Torgersen, Svenn; Wentzel-Larsen, Tore & Ulberg, Randi (2016). Personality disorders and Axis I comorbidity in adolescent outpatients with ADHD. BMC Psychiatry. 16:175, p. 1–10. doi: 10.1186/s12888-016-0871-0. Full text in Research Archive Show summary

  Background Attention deficit hyperactivity disorder (ADHD) is a lifelong condition which carries great cost to society and has an extensive comorbidity. It has been assumed that ADHD is 2 to 5 times more frequent in boys than in girls. Several studies have suggested developmental trajectories that link ADHD and certain personality disorders. The present study investigated the prevalence of ADHD, common Axis I disorders, and their gender differences in a sample of adolescent outpatients. We also wanted to investigate the relationship between ADHD and personality disorders (PDs), as well as how this relationship was influenced by adjustment for Axis I disorders, age and gender. Methods We used a sample consisting of 153 adolescents, aged 14 to 17 years, who were referred to a non-specialized mental health outpatient clinic with a defined catchment area. ADHD, conduct disorder (CD) and other Axis I conditions were assessed using the Mini International Neuropsychiatric Interview (MINI). PDs were assessed using the Structured Interview for DSM-IV Personality (SIDP-IV). Results 13.7 % of the adolescents met diagnostic criteria for ADHD, with no significant gender difference. 21.6 % had at least one PD, 17.6 % had CD, and 4.6 % had both ADHD and a PD. There was a significantly elevated number of PD symptoms in adolescents with an ADHD diagnosis (p = 0.001), and this relationship was not significantly weakened when adjusted for age, gender and other Axis I disorders (p = 0.026). Antisocial (χ 2 = 21.18, p = 0.002) and borderline (χ 2 = 6.15, p = 0.042) PDs were significantly more frequent in girls than in boys with ADHD. Conclusions We found no significant gender difference in the prevalence of ADHD in a sample of adolescents referred to a general mental health outpatient clinic. Adolescent girls with ADHD had more PDs than boys, with antisocial and borderline PDs significantly different. The present study suggests that ADHD in girls in a general outpatient population may be more prevalent than previously assumed. It especially highlights the importance of assessing antisocial and borderline personality pathology in adolescent girls presenting with ADHD symptoms.

• Ask, Helga; Waaktaar, Trine; Seglem, Karoline Brobakke & Torgersen, Svenn (2016). Common Etiological Sources of Anxiety, Depression, and Somatic Complaints in Adolescents: A Multiple Rater twin Study. Journal of Abnormal Child Psychology. ISSN 0091-0627. 44(1), p. 101–114. doi: 10.1007/s10802-015-9977-y. Full text in Research Archive
• Seglem, Karoline Brobakke; Waaktaar, Trine; Ask, Helga & Torgersen, Svenn (2016). Sex differences in genetic and environmental contributions to alcohol consumption from early adolescence to young adulthood. Addiction. ISSN 0965-2140. 111(7), p. 1188–1195. doi: 10.1111/add.13321. Full text in Research Archive
• Reichborn-Kjennerud, Ted; Czajkowski, Nikolai Olavi; Ystrøm, Eivind; Ørstavik, Ragnhild; Aggen, Steven H. & Tambs, Kristian [Show all 12 contributors for this article] (2015). A longitudinal twin study of borderline and antisocial personality disorder traits in early to middle adulthood. Psychological Medicine. ISSN 0033-2917. 45(14), p. 3121–3131. doi: 10.1017/S0033291715001117. Full text in Research Archive
• Korsgaard, Hans Ole; Torgersen, Svenn; Wentzel-Larsen, Tore & ULBERG, RANDI (2015). The Relationship between Personality Disorders and Quality of Life in Adolescent Outpatients. Scandinavian Journal of Child and Adolescent Psychiatry and Psychology. 3(3), p. 180–189. doi: 10.21307/sjcapp-2015-018. Full text in Research Archive Show summary

  Background: During recent years, there has been an increasing focus on the benefits of the early detection and treatment of personality disorders in adolescents. Previous studies of adults have shown that the number of personality disorder criteria met is negatively correlated with a patient’s quality of life and general functioning. Objective: The aim of the present study was to investigate the prevalence of personality disorders, particularly with regard to the correlation between the number of personality disorder criteria fulfilled and self-perceived quality of life. Distribution according to gender and age in a clinical sample of adolescent outpatients were also considered. Method: This study included 153 adolescents between the ages of 14 and 17 years who were referred to a mental health outpatient clinic. Personality disorders were assessed using the Structured Interview for DSM-IV Personality. Quality of life was assessed using the Youth Quality of Life Instrument - Research Version, which is a 41-item questionnaire that covers broad aspects of quality of life. Axis I disorders were assessed using the Mini International Neuropsychiatric Interview. Results: Results demonstrated that 21.6% of the adolescents met the diagnostic criteria for at least one personality disorder. A relationship between the number of personality disorder criteria met and reduced quality of life was found. No significant gender differences with regard to the prevalence of each of the personality disorders were revealed. Adjustment for the presence of Axis I disorders did not appreciably affect these findings Conclusion: The present study indicates that reduced quality of life as a result of the number of personality disorder criteria met affects adolescents in much the same way that it does adults. This further emphasizes the clinical importance of including quality of life assessment as part of the general diagnostic procedures used with adolescents.

• Seglem, Karoline Brobakke; Torgersen, Svenn; Ask, Helga & Waaktaar, Trine (2015). Weak etiologic links between control and the externalizing behaviors delinquency and substance abuse in adolescence. Personality and Individual Differences. ISSN 0191-8869. 75, p. 179–184. doi: 10.1016/j.paid.2014.11.036. Full text in Research Archive Show summary

  Impulsive/disinhibitory personality traits have consistently been associated with externalizing symptomatology such as delinquency and substance use problems, often starting in adolescence. Yet the etiological nature of this co-occurrence is not well understood. Using a classic twin study design with self-report data from 717 male and female twin pairs, aged 15–18 years, a hierarchical psychometric model was examined. In this model the shared variance and etiological structure between control, delinquency and substance abuse symptoms, was modeled through a common externalizing factor. Model fitting indicated that the genetic and environmental influences differed in strength between male and female adolescents. The heritability of the externalizing factor was 45% in males and 10% in females, though neither was statistically different from zero. A statistically significant influence of shared environmental factors was seen for both sexes, 21% in males and 54% in females. In both sexes, the externalizing factor accounted for little variance in control, indicating a weak association and little shared etiology with externalizing liability. These results illuminate further that facets of impulsivity are differentially associated with vulnerability for externalizing symptomatology.

• Torgersen, Svenn (2015). Personlighetsforstyrrelser. In Kennair, Leif Edward Ottesen & Hagen, Roger (Ed.), Personlighetspsykologi. Fagbokforlaget. ISSN 9788245017151. p. 241–264. Full text in Research Archive
• Seglem, Karoline Brobakke; Waaktaar, Trine; Ask, Helga & Torgersen, Svenn (2015). Genetic and Environmental Influences on Adolescents’ Smoking Involvement: A Multi-informant Twin Study. Behavior Genetics. ISSN 0001-8244. 45(2), p. 171–180. doi: 10.1007/s10519-015-9706-x. Full text in Research Archive
• Øvergaard, Kristin Romvig; Aase, Heidi; Torgersen, Svenn; Reichborn-Kjennerud, Ted; Ørbeck, Beate & Myhre, Anne Margrethe [Show all 7 contributors for this article] (2014). Continuity in features of anxiety and attention deficit/hyperactivity disorder in young preschool children. European Child and Adolescent Psychiatry. ISSN 1018-8827. 23(9), p. 743–752. doi: 10.1007/s00787-014-0538-7. Full text in Research Archive Show summary

  Anxiety disorders and Attention Deficit / Hyperactivity Disorder (ADHD) develop before school age, but little is known about early developmental pathways. Here we test two hypotheses: first, that early signs of anxiety and ADHD at 18 months predict symptoms of anxiety and ADHD at age 3½ years; second, that emotional dysregulation at 18 months predicts the outcome of co-occurring anxiety and ADHD at age 3½ years. The study was part of the prospective Norwegian Mother and Child Cohort Study (MoBa) at the Norwegian Institute of Public Health. The 628 participants were clinically assessed at 3½ years. Questionnaire data collected at 18 months were categorized into early behavioural scales of anxiety, ADHD, and emotional dysregulation. We investigated continuity in features of anxiety and ADHD from 18 months to 3½ years of age through logistic regression analyses. Anxiety symptoms at 3½ years were predicted by early signs of anxiety (Odds ratio [OR] = 1.41, CI = 1.15-1.73) and emotional dysregulation (OR = 1.33, CI = 1.15-1.54). ADHD symptoms at 3½ years were predicted by early signs of ADHD (OR = 1.51, CI = 1.30-1.76) and emotional dysregulation (OR = 1.31, CI = 1.13-1.51). Co-occurring Anxiety and ADHD symptoms at 3½ years were predicted by early signs of anxiety (OR = 1.43, CI = 1.13-1.84), ADHD (OR = 1.30, CI = 1.11-1.54), and emotional dysregulation (OR = 1.34, CI = 1.13-1.58). We conclude that there were modest continuities in features of anxiety and ADHD through early preschool years, while emotional dysregulation at age 18 months was associated with symptoms of anxiety, ADHD, and co-occurring anxiety and ADHD at age 3 ½ years.

• Ask, Helga; Torgersen, Svenn; Seglem, Karoline Brobakke & Waaktaar, Trine (2014). Genetic and environmental causes of variation in adolescent anxiety symptoms: A multiple-rater twin study. Journal of Anxiety Disorders. ISSN 0887-6185. 28(4), p. 363–371. doi: 10.1016/j.janxdis.2014.04.003. Full text in Research Archive Show summary

  Heritability estimates for adolescent anxiety vary across studies, partly depending on who is rating thesymptoms. The goal of our study was to estimate genetic and environmental influences using a multi-informant design with responses from a population-based sample of adolescent twins, their mothers andtheir fathers (N = 1394 families).Results from multivariate biometrical modeling indicated quantitative, but no qualitative sex differ-ences in etiology. The best fitting model was an AE Common Pathway model, defining anxiety as a latentfactor common to all informants. This model offers error free estimates of genetic and environmentalinfluences explaining the latent factor variance.Variation in the latent factor was highly genetic, with heritability estimates of 65% for boys and 74%for girls. Non-shared environmental effects explained the remaining variance. In addition, there weresignificant rater-specific genetic and environmental effects for both sexes.The observed rater differences underline the importance of using several informants when studyingadolescent anxiety.

• Holte, Arne; Barry, Margaret M.; Bekkhus, Mona; Borge, Anne Inger Helmen; Bowes, Lucy & Casas, Ferran [Show all 25 contributors for this article] (2014). Psychology of Child Well-Being. In Ben-Arieh, Asher; Casas, Ferran; Frønes, Ivar & Korbin, Jill E. (Ed.), Handbook of child well-being : theories, methods and policies in global perspective. Springer. ISSN 9789048190621. p. 555–631. doi: 10.1007/978-90-481-9063-8_13. Full text in Research Archive
• Villabø, Marianne Aalberg; Gere, Martina Kaja; Torgersen, Svenn; Arnberg, Kasper; Neumer, Simon-Peter & Kendall, Philip C (2013). Anxious Self-Statements in Clinic-Referred US and Norwegian Anxiety-Disordered Youth. Cognitive Therapy and Research. ISSN 0147-5916. 37(4), p. 840–850. doi: 10.1007/s10608-013-9530-7. Full text in Research Archive Show summary

  Examined the relationship between negative self-statements and symptoms of anxiety, depression, and attention-deficit/hyperactivity and functional impairment in two studies of anxiety-disordered youth. Study 1 included 144 anxiety-disordered youth (7–13 years; 54.9 % male) from a university-based research clinic in the USA. Study 2 included 111 treatment-seeking youth (7–13 years; 58.6 % male) from Norwegian community clinics. Results from both studies indicated that total negative self-statements were associated with increased symptoms of anxiety and depression as per child-report. Content specific associations were observed for child-reported symptoms of anxiety but not depression. Associations between child-reported negative self-statements and mother-reported symptoms were mixed. In Study 1, total negative and anxious self-statements were associated with greater functional impairment. The role of negative self-statements in youth’s internalizing symptomatology and the clinical implications are discussed.

• Waaktaar, Trine & Torgersen, Svenn (2013). Self-Efficacy Is Mainly Genetic, Not Learned: A Multiple-Rater Twin Study on the Causal Structure of General Self-Efficacy in Young People. Twin Research and Human Genetics. ISSN 1832-4274. 16(3), p. 651–660. doi: 10.1017/thg.2013.25. Full text in Research Archive Show summary

  Social learning theory postulates that self-efficacy is learned through the person's interaction with his/her physical and social environment. In this genetically informative, population-based, multi-informant study of 1,394 adolescent twin pairs, self-efficacy was modeled as one latent psychometric self-efficacy factor with genetic and environmental effects common to all informants, as well as for effects specific for each informant. The results showed that 75% of variation in self-efficacy was due to genetic factors. Non-shared environmental causes explained the remaining 25% of the variance in the latent factor, with no effect of common environment. Some informant-specific effects were also found. The present study challenges the theoretical assumption of learning as the dominant etiological factor behind self-efficacy in young people.

• Gere, Martina Kaja; Hagen, Kristine Amlund; Villabø, Marianne Aalberg; Arnberg, Kasper; Neumer, Simon-Peter & Torgersen, Svenn (2013). Father's mental health as a protective factor in the relationship between maternal and child depressive symptoms. Depression and Anxiety. ISSN 1091-4269. 30(1), p. 31–38. doi: 10.1002/da.22010. Full text in Research Archive Show summary

  Background: The relationship between parental and child depressive symptoms has been found to be stronger for mothers than for fathers. Does this mean that fathers’ mental health is less important in the context of child depressive symptoms? The goal of the current study is to test whether the degree of fathers’ depressive symptoms moderate the relationship between mothers’ and children's depressive symptoms. Our knowledge about such interaction effects between mothers’ and fathers’ symptoms is limited. Methods: We examined depressive symptoms in 190 children (age 7–13, 118 boys) referred to child community clinics and their parents. Mothers and fathers reported on their own and their child's depressive symptoms, whereas children only reported on their own symptoms. Results: Structural equation modeling revealed significant interaction effects of mothers’ and fathers’ depressive symptoms on mother- and father-reported child depressive symptoms, while no effects were found for child reports. When fathers reported few depressive symptoms for themselves, no relationship between mothers’ and children's depressive symptoms was observed. The more depressive symptoms in fathers, the stronger the relationship between mothers’ and children's symptoms. Conclusions: Fathers’ mental health may be a protective factor in the relationship between mothers’ and children's depressive symptoms. Thus, researchers and practitioners would benefit from considering not only depressive symptoms in mothers, but also in fathers, when examining and working with child depressive symptoms.

• Bjørnebekk, Astrid; Fjell, Anders Martin; Walhovd, Kristine B; Grydeland, Håkon; Torgersen, Svenn & Westlye, Lars Tjelta (2013). Neuronal correlates of the five factor model (FFM) of human personality: Multimodal imaging in a large healthy sample. NeuroImage. ISSN 1053-8119. 65, p. 194–208. doi: 10.1016/j.neuroimage.2012.10.009. Full text in Research Archive Show summary

  Advances in neuroimaging techniques have recently provided glimpse into the neurobiology of complex traits of human personality. Whereas some intriguing findings have connected aspects of personality to variations in brain morphology, the relations are complex and our current understanding is incomplete. Therefore, we aimed to provide a comprehensive investigation of brain–personality relations using a multimodal neuroimaging approach in a large sample comprising 265 healthy individuals. The NEO Personality Inventory was used to provide measures of core aspects of human personality, and imaging phenotypes included measures of total and regional brain volumes, regional cortical thickness and arealization, and diffusion tensor imaging indices of white matter (WM) microstructure. Neuroticism was the trait most clearly linked to brain structure. Higher neuroticism including facets reflecting anxiety, depression and vulnerability to stress was associated with smaller total brain volume, widespread decrease in WM microstructure, and smaller frontotemporal surface area. Higher scores on extraversion were associated with thinner inferior frontal gyrus, and conscientiousness was negatively associated with arealization of the temporoparietal junction. No reliable associations between brain structure and agreeableness and openness, respectively, were found. The results provide novel evidence of the associations between brain structure and variations in human personality, and corroborate previous findings of a consistent neuroanatomical basis of negative emotionality.

• Villabø, Marianne Aalberg; Cummings, Colleen M.; Gere, Martina Kaja; Torgersen, Svenn & Kendall, Philip C (2013). Anxious youth in research and service clinics. Journal of Anxiety Disorders. ISSN 0887-6185. 27(1), p. 16–24. doi: 10.1016/j.janxdis.2012.09.003. Full text in Research Archive Show summary

  With the current focus on increasing utilization of empirically-supported treatments, knowledge of sample differences and similarities has increasing importance. The present study compared anxiety-disordered youth (age 7-13) from (a) five Norwegian service clinics (SC, N = 111) to (b) a university research clinic (RC) in Philadelphia, USA (N = 144) on pre-treatment characteristics measured by the Multidimensional Anxiety Scale for Children, Child Behavior Checklist, Teacher Report Form, Anxiety Disorders Interview Schedule, and Children's Global Assessment Scale (CGAS). SC youth demonstrated higher levels of anxiety based on child- (d =0.42-1.04) and parent-report (d = 0.53) and conduct problems based on parent-report (d = 0.43) compared to RC youth. SC youth was more functionally impaired on the CGAS (d = 0.97), whereas RC youth evidenced a greater number of diagnoses (d = 0.63). The two samples were equivalent regarding parent-reported symptoms of affective, somatic, attention-deficit/hyperactivity, and oppositional problems. Future directions and clinical implications are discussed.

• Torgersen, Svenn; Myers, John; Reichborn-Kjennerud, Ted; Røysamb, Espen; Kubarych, Thomas S. & Kendler, Kenneth S. (2012). The heritability of cluster B personality disorders assessed both by personal interview and questionnaire. Journal of Personality Disorders. ISSN 0885-579X. 26(6), p. 848–866. doi: 10.1521/pedi_2012_26_060. Full text in Research Archive Show summary

  Whereas the heritability of common personality traits has been firmly established, the results of the few published studies on personality disorders (PDs) are highly divergent, with some studies finding high heredity and others very low. A problem with assessing personality disorders by means of interview is errors connected with interviewer bias. A way to overcome the problem is to use self-report questionnaires in addition to interviews. This study used both interview and questionnaire for assessing DSM-IV Cluster B personality disorders: antisocial personality disorder (APD), borderline (BPD), narcissistic (NPD), and histrionic (HPD). We assessed close to 2,800 twins from the Norwegian Institute of Public Health Twin Panel using a self-report questionnaire and, a few years later, the Structured Interview for DSM-IV Personality (SIDP-IV). Items from the self-report questionnaire that best predicted the PDs captured by the interview were then selected. Measurement models combining questionnaire and interview information were applied and were fitted using Mx. Whereas the heritability of Cluster B PDs assessed by interview was around .30, and around .40–.50 when assessed by self-report questionnaire, the heritability of the convergent latent factor, including information from both interview and self-report questionnaire was .69 for APD, .67 for BPD, .71 for NPD, and .63 for HPD. As is usually found for personality, the effect of shared-in families (familial) environment was zero. In conclusion, when both interview and self-report questionnaire are taken into account, the heritability of Cluster B PD appears to be in the upper range of previous findings for mental disorders.

• Torgersen, Svenn (2012). Epidemiology. In Widiger, Thomas A. (Eds.), The Oxford handbook of personality disorders. Oxford University Press. ISSN 9780199735013. p. 186–205. Full text in Research Archive Show summary

  On the cusp of the newest edition of the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders (DSM), the field of personality disorders is thriving and productive. This is certainly a time of major transition for the classification, study, and treatment of personality disorders, as the personality disorders section of the DSM is undergoing major revision, leaving researchers and clinicians to wonder whether their area of specialty in the field of personality disorders will be retained, deleted, or revised in DSM-5. In advance of DSM-5, The Oxford Handbook of Personality Disorders provides a summary of the latest information concerning the diagnosis, assessment, construct validity, etiology, pathology, and treatment of personality disorders. The text looks at personality disorders proposed for retention in DSM-5. It also investigates personality disorders that are slated for deletion. The book further examines issues concerning three disorders that have never obtained or had previously lost official recognition (i.e., passive-aggressive, depressive, and racist). The book also includes articles authored by members of the DSM-5 Personality Disorders Work Group, which succinctly outline and explain the proposals, as well as articles by authors who raise significant questions and concerns (often differing) about these proposals. The text includes special coverage of largely neglected areas of investigation (i.e. childhood antecedents of personality disorder, cross-cultural validity). The book finally looks into controversial areas for the DSM, such as schizotypal personality disorder, narcissism, depressive personality disorder, dependent personality disorder, and dimensional classification

• Gere, Martina Kaja; Villabø, Marianne Aalberg; Torgersen, Svenn & Kendall, Philip C (2012). Overprotective parenting and child anxiety: The role of co-occurring child behavior problems. Journal of Anxiety Disorders. ISSN 0887-6185. 26(6), p. 642–649. doi: 10.1016/j.janxdis.2012.04.003. Full text in Research Archive Show summary

  The relationship between overprotective parenting and child anxiety has been examined repeatedly because theories emphasize its role in the maintenance of child anxiety. No study has yet tested whether this relationship is unique to child anxiety, by controlling for commonly co-occurring behavior problems within the same children. The current study examined 190 children (age 7-13, 89 boys) referred to mental health clinics and their parents. Results revealed that significant correlations between overprotective parenting and child anxiety symptoms disappear after controlling for co-occurring child behavior symptoms. It appears that overprotection is not uniquely related to child anxiety. Furthermore, overprotective parenting was significantly and uniquely related to child behavior symptoms. Researchers and practitioners need to consider co-occurring child behavior problems when working with the parents of anxious children.

• Waaktaar, Trine & Torgersen, Svenn (2012). Genetic and Environmental Causes of Variation in Trait Resilience in Young People. Behavior Genetics. ISSN 0001-8244. 42(3), p. 366–377. doi: 10.1007/s10519-011-9519-5. Full text in Research Archive Show summary

  The aim of this multi-informant twin study was to determine the relative role of genetic and environmental factors in explaining variation in trait resilience in adolescents. Participants were consenting families (N = 2,638 twins in 1,394 families), from seven national cohorts (age 12-18 years, both sexes) of monozygotic and dizygotic twins reared together. Questionnaire data on the adolescents' Ego-resilience (ER89) was collected from mothers, fathers and twins, and analysed by means of multivariate genetic modelling. Variance in trait resilience was best represented in an ADE common pathways model with sex limitation. Variance in the latent psychometric resilience factor was largely explained by additive genetic factors (77% in boys, 70% in girls), with the remaining variance (23 and 30%) attributable to non-shared environmental factors. Additive genetic sources explained more than 50% of the informant specific variation in mothers and fathers scores. In twins, additive and non-additive genetic factors together explained 40% and non-shared environmental factor the remaining 60% of variation. In the mothers' scores, the additive genetic effect was larger for boys than for girls. The non-additive genetic factor found in the twins' self ratings was larger in boys than in girls. The remaining sex differences in the specific factors were small. Trait resilience is largely genetically determined. Estimates based on several informants rather than single informants approaches are recommended

• Waaktaar, Trine & Torgersen, Svenn (2012). Genetic and environmental causes of variation in perceived loneliness in young people. American Journal of Medical Genetics Part B: Neuropsychiatric Genetics. ISSN 1552-4841. 159B(5), p. 580–588. doi: 10.1002/ajmg.b.32064. Full text in Research Archive Show summary

  Loneliness is prevalent in adolescence, despite the widespread expectation directed to young people to start building close relationships beyond the nuclear family. The aim of the present study was to explore the causal genetic and environmental structure behind variability in adolescents' perceived loneliness. Seven national cohorts (ages 12–18 years) of Norwegian twins reared together (1,394 twin pairs) participated. Perceived loneliness was measured with five items from the UCLA Loneliness Scale. Data were collected from mothers, fathers, and twins' self ratings by means of a posted questionnaire. Biometric analyses were applied, testing the causal architecture of loneliness within a psychometric model with one common latent factor in addition to specific genetic and environmental sources influencing the scores of each informant. The results showed a heritability (h2) of 75% on the latent perceived loneliness factor, and nonshared environmental effects (e2) explaining the remaining 25% of the latent factor variance. There were also significant rater-specific genetic and nonshared environmental effects. No shared environmental effects were found in the model, and there were no sex differences in the estimates. This study showed that variation in perceived loneliness in adolescents is highly genetic. Additional genetic and nonshared environmental etiological sources are to some extent represented in the scores of the specific rater.

• Gjerde, Line Cecilie; Czajkowski, Nikolai Olavi; Røysamb, Espen; Ørstavik, Ragnhild; Knudsen, Gun Peggy & Østby, Kristian Roald Amundsen [Show all 10 contributors for this article] (2012). The heritability of avoidant and dependent personality disorder assessed by personal interview and questionnaire. Acta Psychiatrica Scandinavica. ISSN 0001-690X. 126(6), p. 448–457. doi: 10.1111/j.1600-0447.2012.01862.x. Full text in Research Archive Show summary

  Objective:  Personality disorders (PDs) have been shown to be modestly heritable. Accurate heritability estimates are, however, dependent on reliable measurement methods, as measurement error deflates heritability. The aim of this study was to estimate the heritability of DSM-IV avoidant and dependent personality disorder, by including two measures of the PDs at two time points. Method:  Data were obtained from a population-based cohort of young adult Norwegian twins, of whom 8045 had completed a self-report questionnaire assessing PD traits. 2794 of these twins subsequently underwent a structured diagnostic interview for DSM-IV PDs. Questionnaire items predicting interview results were selected by multiple regression, and measurement models of the PDs were fitted in Mx. Results:  The heritabilities of the PD factors were 0.64 for avoidant PD and 0.66 for dependent PD. No evidence of common environment, that is, environmental factors that are shared between twins and make them similar, was found. Genetic and environmental contributions to avoidant and dependent PD seemed to be the same across sexes. Conclusion:  The combination of both a questionnaire- and an interview assessment of avoidant and dependent PD results in substantially higher heritabilities than previously found using single-occasion interviews only.

• Villabø, Marianne Aalberg; Gere, Martina Kaja; Torgersen, Svenn; March, John S & Kendall, Philip C (2012). Diagnostic efficiency of the child and parent versions of the Multidimensional Anxiety Scale for Children. Journal of Clinical Child & Adolescent Psychology. ISSN 1537-4416. 41(1), p. 75–85. doi: 10.1080/15374416.2012.632350. Full text in Research Archive Show summary

  The objective of this study is to evaluate the psychometrics and clinical efficiency of the Multidimensional Anxiety Scale for Children (MASC), which measures physical symptoms, harm avoidance, social anxiety, and separation/panic. Using a sample of 190 treatment-seeking Norwegian youth (aged 7-13 years, M (age) = 10.3 years, 62.1% male), the internal stability and ability to predict to disorder were examined for child, mother, and father reports on the MASC. Moderate to strong internal reliability was exhibited across all MASC subscales. Parent-child agreement was low, but mother-father agreement was high. MASC scores successfully distinguished between children with and without anxiety disorders and identified youth with separation anxiety disorder and social phobia, but less accurately generalized anxiety disorders. The MASC has favorable psychometric properties and is a useful screening instrument for identifying youth with anxiety disorders

• Røysamb, Espen; Kendler, Kenneth S; Tambs, Kristian; Ørstavik, Ragnhild; Aggen, Steven H & Neale, Michael C [Show all 8 contributors for this article] (2011). The joint structure of DSM-IV Axis I and Axis II disorders. Journal of Abnormal Psychology. ISSN 0021-843X. 120(1), p. 198–209. doi: 10.1037/a0021660. Full text in Research Archive
• Waaktaar, Trine & Torgersen, Svenn (2010). How resilient are resilience scales? The Big Five scales outperform resilience scales in predicting adjustment in adolescents. Scandinavian Journal of Psychology. ISSN 0036-5564. 51(2), p. 157–163. doi: 10.1111/j.1467-9450.2009.00757.x. Full text in Research Archive
• Cramer, Victoria; Torgersen, Svenn & Kringlen, Einar (2010). Mood disorders and quality of life. A community study. Nordic Journal of Psychiatry. ISSN 0803-9488. 64(1), p. 58–62. doi: 10.3109/08039480903287565. Full text in Research Archive
• Reichborn-Kjennerud, Ted; Czajkowski, Nikolai; Røysamb, Espen; Ørstavik, Ragnhild Elise; Neale, Michael C & Torgersen, Svenn [Show all 7 contributors for this article] (2010). Major depression and dimensional representations of DSM-IV personality disorders: a population-based twin study. Psychological Medicine. ISSN 0033-2917. 40(9), p. 1475–1484. doi: 10.1017/S0033291709991954. Full text in Research Archive
• Torgersen, Svenn (2009). Det psykiatriske intervju, Det kliniske intervjuet. Gyldendal Akademisk. Full text in Research Archive
• Edvardsen, Jack; Torgersen, Svenn; Røysamb, Espen; Lygren, Sissel; Skre, Ingunn & Onstad, Sidsel [Show all 10 contributors for this article] (2009). Unipolar depressive disorders have a common genotype. Journal of Affective Disorders. ISSN 0165-0327. 117(1-2), p. 30–41. doi: 10.1016/j.jad.2008.12.004. Full text in Research Archive
• Tambs, Kristian; Rønning, Torbjørn; Prescott, CA; Kendler, Kenneth S; Reichborn-Kjennerud, Ted & Torgersen, Svenn [Show all 7 contributors for this article] (2009). The Norwegian Institute of Public Health Twin Study of Mental Health: Examining recruitment and attrition bias. Twin Research and Human Genetics. ISSN 1832-4274. 12(2), p. 158–168. Full text in Research Archive
• Torgersen, Svenn (2009). The nature (and nurture) of personality disorders. Scandinavian Journal of Psychology. ISSN 0036-5564. 50(6), p. 624–632. doi: 10.1111/j.1467-9450.2009.00788.x. Full text in Research Archive
• Vollrath, Margarete E. & Torgersen, Svenn (2008). Personality types and risky health behaviors in Norwegian students. Scandinavian Journal of Psychology. ISSN 0036-5564. 49(3), p. 287–292. doi: 10.1111/j.1467-9450.2008.00631.x. Full text in Research Archive
• Edvardsen, Jack; Torgersen, Svenn; Røysamb, Espen; Lygren, Sissel; Skre, Ingunn & Onstad, Sidsel [Show all 7 contributors for this article] (2008). Heritability of bipolar spectrum disorders. Unity or heterogeneity? Journal of Affective Disorders. ISSN 0165-0327. 106(3), p. 229–240. doi: 10.1016/j.jad.2007.07.001. Full text in Research Archive
• Torgersen, S; Czajkowski, Nikolai; Jacobson, K; Reichborn-Kjennerud, Ted; Røysamb, Espen & Neale, MC [Show all 7 contributors for this article] (2008). Dimensional representations of DSM-IV cluster B personality disorders in a population-based sample of Norwegian twins: a multivariate study. Psychological Medicine. ISSN 0033-2917. 38(11), p. 1617–1625. doi: 10.1017/S0033291708002924. Full text in Research Archive
• Torgersen, Svenn (2008). Obsessive compulsive disorder plus schizotypal personality disorder: Is the sum more than the parts? Personality and Mental Health. ISSN 1932-8621. 2, p. 204–206. Full text in Research Archive
• Kristensen, Hanne & Torgersen, Svenn (2008). Is social anxiety disorder in childhood associated with developmental deficit/delay? European Child and Adolescent Psychiatry. ISSN 1018-8827. 17(2), p. 99–107. doi: 10.1007/s00787-007-0642-z. Full text in Research Archive Show summary

  Children with social anxiety disorder (SAD) have been reported to display reduced social skills. Less attention has been paid to whether neurodevelopmental deficits/delays (NDD’s) in language and motor function may contribute to their impaired social skills. The present study aimed to assess the extent of language and motor impairment in children with SAD. A population-based screened sample consisting of 150 children (11–12 years) was assessed with a diagnostic interview (Kiddie-SADS), the Wechsler Abbreviated Scale of Intelligence (WASI) and the Motor Assessment Battery for Children (MABC). Test results were compared across five diagnostic groups: SAD (n = 29); ADHD (n = 23); SAD and ADHD (n = 6); “other disorder” (n = 44) and “no disorder” (n = 48). Delays in language and motor development as reported by mother were also investigated. Verbal IQ and motor skills were reduced and maternally reported delay was more frequent in the SAD group compared to the “other disorder” and “no disorder” group.

• Torgersen, Svenn (2008). The genetic epidemiology of major depression. Actas espanolas de psiquiatria. ISSN 1139-9287. 36, p. 25–27. Full text in Research Archive
• Kendler, Kenneth S; Aggen, Steven H; Czajkowski, Nikolai; Røysamb, Espen; Tambs, Kristian & Torgersen, Svenn [Show all 8 contributors for this article] (2008). The structure of genetic and environmental risk factors for DSM-IV personality disorders: a multivariate twin study. Archives of General Psychiatry. ISSN 0003-990X. 65(12), p. 1438–1446. Full text in Research Archive
• Torgersen, Svenn & Waktaar, Trine (2007). Resiliens som personlighetsbegrep. In Borge, Anne Inger Helmen (Eds.), Resiliens i praksis. Teori og empiri i et norsk perspektiv. Gyldendal Akademisk. ISSN 9788205359352. p. 52–74. Full text in Research Archive
• Cramer, Victoria; Torgersen, Svenn & Kringlen, Einar (2007). Socio-demographic conditions, subjective somatic health, axis I disorders and personality disorders in the common population: The relationship to quality of life. Journal of Personality Disorders. ISSN 0885-579X. 21, p. 552–567. Full text in Research Archive
• Kristensen, Hanne & Torgersen, Svenn (2007). The association between avoidant personality traits and motor impairment in a population-based sample of 11-12-year-old children. Journal of Personality Disorders. ISSN 0885-579X. 21(1), p. 87–98. doi: 10.1521/pedi.2007.21.1.87. Full text in Research Archive Show summary

  The aim of the study was to examine the association between avoidant personality traits and motor impairment in childhood. The relationship between other personality traits and motor function was also explored. A population-based screened sample of 150 11-12-year-old children (50 socially anxious, 50 impulsive and 50 nonsocially anxious/nonimpulsive) was assessed using the Coolidge Personality and Neuropsychological Inventory for Children (CPNI) and the Motor Assessment Battery for Children (MABC). Among the personality scales, avoidant personality traits were most strongly associated with motor impairment. Children with clinically avoidant personality traits (n = 31) showed a significantly poorer motor performance than children in the nonclinical avoidance group (n = 119). About 50% of the children with clinical avoidance obtained a motor score below the 5th percentile. No gender differences in motor performance were found in the clinical avoidance group. More research on the impact of motor impairment on psychological development is needed.

• Reichborn-Kjennerud, Ted; Czajkowski, Nikolai; Neale, Michael C.; Ørstavik, Ragnhild Elise; Torgersen, Svenn & Tambs, Kristian [Show all 9 contributors for this article] (2007). Genetic and environmental influences on dimensional representations of DSM-IV cluster C personality disorders: a population-based multivariate twin study. Psychological Medicine. ISSN 0033-2917. 37(5), p. 645–653. doi: 10.1017/S0033291706009548. Full text in Research Archive
• Battaglia, Marco; Ogliari, Anna; Harris, Jennifer; Spatola, Chiara AM; Pesenti-Gritti, Paola & Reichborn-Kjennerud, Ted [Show all 9 contributors for this article] (2007). A genetic study of the acute anxious response to carbon dioxide stimulation in man. Journal of Psychiatric Research. ISSN 0022-3956. 41(11), p. 906–917. doi: 10.1016/j.jpsychires.2006.12.002. Full text in Research Archive
• Reichborn-Kjennerud, Ted; Czajkowski, Nikolai; Torgersen, Svenn; Neale, Michael C.; Ørstavik, Ragnhild Elise & Tambs, Kristian [Show all 7 contributors for this article] (2007). The relationship between avoidant personality disorder and social phobia: A population-based twin study. American Journal of Psychiatry. ISSN 0002-953X. 164(11), p. 1722–1728. doi: 10.1176/appi.ajp.2007.06101764. Full text in Research Archive
• Kendler, KS; Myers, J; Myers, John; Torgersen, Svenn; Neale, MC & Reichborn-Kjennerud, Ted (2007). The heritability of cluster A personality disorders assessed by both personal interview and questionnaire. Psychological Medicine. ISSN 0033-2917. 37. doi: 10.1017/S0033291706009755. Full text in Research Archive
• Lau, Bjørn; Hem, Erlend; Berg, Anne Marie Lie; Ekeberg, Øivind & Torgersen, Svenn (2006). Personality types, coping, and stress in the Norwegian police service. Personality and Individual Differences. ISSN 0191-8869. 41(5), p. 971–982. doi: 10.1016/j.paid.2006.04.006. Full text in Research Archive Show summary

  Much research has been undertaken to determine what characterizes the ‘police personality’, but so far the results have been ambiguous. We conducted a comprehensive nationwide questionnaire survey of 3272 Norwegian police personnel at all ranks, using a short form of the Basic Character Inventory, Job Stress Survey, and Coping Strategies Scale. We combined the three personality traits of Neuroticism, Extraversion, and Conscientiousness into eight personality types: the spectator, insecure, sceptic, brooder, hedonist, impulsive, entrepreneur, and complicated. The results showed that entrepreneur and hedonist personality types, characterized by a combination of high values on Extraversion and low values on Neuroticism, reported lower values on perceived stress compared to others, whereas the insecure and brooder types, which combine low Extraversion with high values on Neuroticism, reported higher levels on perceived stress. Further, the entrepreneur and complicated types reported higher values on active coping strategies, whereas those combining low Extraversion and low Conscientiousness reported either less control coping (the insecure type), or support coping (the spectator type) compared to others. The findings indicate that a typology approach may be fruitful in exploring how police personnel with different combinations of personality traits experience and cope with stress.

• Torgersen, Svenn (2006). Genetische Aspekte Narzisstischer Persønlichkeitsstørungen. In Kernberg, Otto F & Hartmann, Hans-Peter (Ed.), Narzissmus Grundlagen - Størungsbilder - Therapie. Schattauer Gmbh. ISSN 9783794524662. p. 432–436. Full text in Research Archive
• Torgersen, Svenn & Vollrath, Margarete E. (2006). Personality types, personality traits, and risky health behavior. In Vollrath, Margarete E. (Eds.), Handbook of Personality and Health. John Wiley & Sons. ISSN 9780470021354. p. 215–234. Full text in Research Archive
• Torgersen, Svenn (2006). Keep it in the family. Nature. ISSN 0028-0836. 442(138). Full text in Research Archive
• Kendler, KS; Czajkowski, Nikolai; Tambs, Kristian; Torgersen, Svenn; Aggen, SH & Neale, Michael C. [Show all 7 contributors for this article] (2006). Dimensional representations of DSM-IV Cluster A personality disorders in a population-based sample of Norwegian twins: a multivariate study. Psychological Medicine. ISSN 0033-2917. 36(11), p. 1583–1591. doi: 10.1017/S0033291706008609. Full text in Research Archive
• Cramer, Victoria; Torgersen, Svenn & Kringlen, Einar (2006). Personality disorder and quality of life. Comprehensive Psychiatry. ISSN 0010-440X. 47, p. 178–184. Full text in Research Archive
• Torgersen, Svenn & Vollrath, Margarete Erika (2006). Personality types, personality traits, and risky health behaviors. In Vollrath, Margarete E. (Eds.), Handbook of personality and health. John Wiley & Sons. ISSN 9780470021347. p. 215–233. Full text in Research Archive
• Kristensen, Hanne & Torgersen, Svenn (2006). Social anxiety disorder in 11-12-year-old children. The efficacy of screening and issues in parent-child agreement. European Child and Adolescent Psychiatry. ISSN 1018-8827. 15(3), p. 163–171. doi: 10.1007/s00787-005-0519-y. Full text in Research Archive Show summary

  Objective: To investigate the level of diagnostic and discriminative accuracy of The Social Anxiety Scale for Children – Revised (SASC-R) for identifying social anxiety disorder (SAD) in a community-based sample of 11–12 year-old children. Parent–child diagnostic agreement was also examined. Method: A questionnaire including SASC-R and items on impulsive behavior was sent to a population based sample of children, born in 1992. A total of 2568 parents returned their questionnaires (rr: 70%), and 1297 (51%) consented to further participation. An index group [50 high-scoring children on social anxiety (SA-group)] and two contrast groups [(50 high-scoring children on impulsive behavior (Imp-group) and 50 low-scoring children on SA and Imp, (Ls-group)] were selected for participation. Results: SAD was assigned 35 (23%) of 150 children; 28 (80%) from the SA-group; 7 (20%) from the Imp- group and 0 from the Ls-group. The SASC-R showed relatively high discriminative accuracy for SAD, but was also influenced by other diagnoses. Mother–child agreement was fair (κ=0.46), and mother-only diagnoses were frequent. Both child and parent information are important when diagnosing SAD in this age group.

• Waaktaar, Trine; Avdem, Jorid & Torgersen, Svenn (2006). Forebygging av vansker hos ungdom - hva kan vi lære av resiliensforskning? In Kleven, Karin; Talseth, Randi; Notøy, Ingunn & Vea, Ingeborg (Ed.), Barn i Norge 2006. Barn i risiko. Voksne for barn. ISSN 9788292488089. p. 27–34. Full text in Research Archive
• Kringlen, Einar; Torgersen, Svenn & Cramer, Victoria (2006). Mental illness in a rural area - A Norwegian psychiatric epidemiological study. Social Psychiatry and Psychiatric Epidemiology. ISSN 0933-7954. 41, p. 713–719. Full text in Research Archive
• Torgersen, Svenn (2005). Epidemiology. In Oldham, John M; Skodol, Andrew E & Bender, Donna S (Ed.), The American Psychiatric Publishing Textbook of Personality Disorders. American Psychiatric Association Publishing. ISSN 9781585621590. p. 129–142. Full text in Research Archive
• Helgeland, MI & Torgersen, Svenn (2005). Stability and prediction of schizophrenia from adolescence to adulthood. European Child and Adolescent Psychiatry. ISSN 1018-8827. 14. Full text in Research Archive
• Cramer, Victoria; Torgersen, Svenn & Kringlen, E (2005). Quality of life and anxiety disorders: A population study. Journal of Nervous and Mental Disease. ISSN 0022-3018. 193. Full text in Research Archive
• Torgersen, Svenn (2005). Genetics of Borderline Personality Disorder. In Zanarini, Mary C (Eds.), Borderline Personality Disorder. Taylor & Francis. ISSN 9780824729288. p. 127–134. Full text in Research Archive
• Helgeland, Margareth Winther; Kjelsberg, Ellen & Torgersen, Svenn (2005). Continuities between emotional and disruptive behavior disorders in adolescence and personality disorders in adulthood. American Journal of Psychiatry. ISSN 0002-953X. 162, p. 1941–1947. Full text in Research Archive
• Torgersen, Svenn (2005). Borderline and histrionic personality disorder. In Maj, Mario (Eds.), Evidence and experince in psychiatry. Vol. 8. Personality disorders. John Wiley & Sons. Full text in Research Archive
• Torgersen, Svenn (2005). Schizotypal personality disorder. In Rønningstam, Elsa & Simonsen, Erik (Ed.), Personality disorders. World Psychiatric Association. Full text in Research Archive
• Waaktaar, Trine; Borge, Anne Inger Helmen; Christie, Helen & Torgersen, Svenn (2005). Youth-parent consistencies on ratings of difficulties and prosocial behaviour: Exploration of an at-risk sample. Scandinavian Journal of Psychology. ISSN 0036-5564. 46(2), p. 179–188. doi: 10.1111/j.1467-9450.2005.00447.x. Full text in Research Archive Show summary

  Low informant agreement is of particular concern in clinical settings, since diagnoses and interventions are largely based on reports from parents and/or youths. This study explores youth-parent consistencies in an at-risk sample of youths (n= 42), several from immigrant and refugee families, all with stressful background experiences. Data from a community sample (n= 165) was used to contrast the clinical results. Results showed that correlations between clinical youths and parents were within the same range as those in the community sample. Consistencies concerning absolute level of behavior were higher in the clinical sample. However, interesting differences in informant consistencies were found on difficulties and resources between the two samples. This study adds to the picture that there is no simple relationship between severity of behavior deviance and informant agreement. Asking about behavioral resources as well as difficulties may provide valuable additional information regarding differences in the perspectives of at-risk youths and parents.

• Torgersen, Svenn (2005). Behavior genetics of personality. Current Psychiatry Reports. ISSN 1523-3812. 7, p. 51–56. Full text in Research Archive
• Waaktaar, Trine; Borge, Anne Inger Helmen; Fundingsrud, Hans Petter; Christie, Helen & Torgersen, Svenn (2004). The role of stressful life events in the development of depressive symptoms in adolescence. Journal of Adolescence. ISSN 0140-1971. 27(2), p. 153–163. Full text in Research Archive

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• Torgersen, Svenn (2008). Personlighet og personlighetsforstyrrelser. Gyldendal Akademisk. ISBN 9788205365391. 351 p. Full text in Research Archive

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• Reichborn-Kjennerud, Ted; Czajkowski, Nikolai Olavi; Ystrøm, Eivind; Ørstavik, Ragnhild; Aggen, Steven H. & Tambs, Kristian [Show all 12 contributors for this article] (2015). Borderline and antisocial personality disorder traits in early to middle adulthood: A longitudinal twin study. Full text in Research Archive Show summary

  Background and Aims: Antisocial personality disorder (ASPD) and borderline personality disorder (BPD) share genetic and environmental risk factors. Little is known about the temporal stability of these etiological factors in adulthood. Methods: DSM-IV criteria for ASPD and BPD were assessed using structured interviews in 2,282 Norwegian twins in early adulthood and approximately 10 years later. Longitudinal biometric models were used to analyze the number of endorsed criteria. Results: The mean criterion count for ASPD and BPD decreased 40% and 28% respectively from early to middle adulthood. Rank-order stability was 0.58 for ASPD and 0.45 for BPD. The best-fitting longitudinal twin model included only genetic and individual-specific environmental factors. Genetic effects, both those shared by ASPD and BPD, and those specific to each disorder remained completely stable. The unique environmental effects, however, changed substantially, with a correlation across time of 0.19 for the shared effects, and 0.39 and 0.15 respectively for those specific to ASPD and BPD. Genetic effects accounted for 71% and 72% of the stability over time for ASPD and BPD respectively. The genetic and environmental correlations between ASPD and BPD were 0.73, and 0.43 respectively at both time points. Conclusion: ASPD and BPD traits were moderately stable from early to middle adulthood, mostly due to genetic risk factors which did not change over the10 year assessment period. Environmental risk factors were mostly transient, and appear to be the main source of phenotypic change. Genetic liability factors were, to a large extent, shared by ASPD and BPD.

• Ask, Helga; Waaktaar, Trine; Seglem, Karoline Brobakke & Torgersen, Svenn (2014). Causes of co-occurring somatic, anxious and depressive symptoms in adolescents. Full text in Research Archive
• Seglem, Karoline Brobakke; Torgersen, Svenn; Ask, Helga & Waaktaar, Trine (2014). Impulsivity, delinquency and substance abuse in adolescence – Can common genetic or environmental factors explain why these traits often co-occur? Full text in Research Archive
• Torgersen, Svenn (2012). Paranoid schizofreni, paranoide psykoser og personlighetsforstyrrelser. 132, p. 851–852. doi: 10.4045/tidsskr.12.0318. Full text in Research Archive
• Jørgensen, Liv & Torgersen, Svenn (2011). I stor grad født sånn. [Internet]. forskning.no. Full text in Research Archive
• Reichborn-Kjennerud, Ted; Czajkowski, Nikolai; Røysamb, Espen; Ørstavik, Ragnhild Elise; Torgersen, Svenn & Kendler, Kenneth S (2009). Major Depression and DSM-IV Personality Disorders: A Population-Based Twin Study. Full text in Research Archive
• Waaktaar, Trine & Torgersen, Svenn (2007). Kapittel 8 Resiliens og intervensjon. In Borge, Anne Inger Helmen (Eds.), Resiliens i praksis : teori og empiri i et norsk perspektiv. Gyldendal Akademisk. ISSN 9788205359352. Full text in Research Archive
• Torgersen, Svenn & Waaktaar, Trine (2007). Resiliens som personlighetsegenskap. In Borge, Anne Inger Helmen (Eds.), Resiliens i praksis : teori og empiri i et norsk perspektiv. Gyldendal Akademisk. ISSN 9788205359352. p. 52–74. Full text in Research Archive
• Torgersen, Svenn (2006). Genes and behavior: Nature-nurture interplay explained. Nature. ISSN 0028-0836. 442, p. 138–138. Full text in Research Archive
• Gere, Martina Kaja; Torgersen, Svenn & Neumer, Simon-Peter (2013). Parent factors in child psychopathology. Overprotective parenting behaviors and parental symptoms of depression and stress. Universitetet i Oslo. Full text in Research Archive
• Aalberg, Marianne; Torgersen, Svenn & Neumer, Simon-Peter (2013). Evidence-based assessment of anxiety-disordered children: From research to community clinics. Universitetet i Oslo. Full text in Research Archive

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