Background. Structural characteristics of social networks such as primary group size have received less attention than measures of perceived social support. Previous research suggests that associations between social network size and later common mental disorder status may differ according to sex and initial mental state.

Method. Adults participating in the 2000 British National Household Survey of psychiatric morbidity were randomly selected for follow-up 18 months later. The revised Clinical Interview Schedule (CIS-R) and the Interview Measure of Social Relations (IMSR) were administered at baseline and follow-up. Primary group size was defined as the total number of close relatives and friends. A four-level scale of common mental disorder was modelled with ordinal logistic regression, based on weighted data (n=2413).

Findings. After adjusting for confounders, a primary group size of three or less at time 1 predicted worse mental health at time 2. This effect was greatest in men who were initially non-cases at baseline (averaged odds 4·5) and in women who were initially cases at baseline (average odds 2·9). Primary group size at time 2 was significantly predicted by level of common mental disorder at time 1 in women but not in men. Thus, confounding by baseline disorder does not explain risk of developing poor mental health in socially isolated men.

Conclusion. This study replicates the strong effects of primary group size on future mental health that emerge when men and women are studied separately and when subjects are categorized according to baseline mental health status.

Background. Depression in women is associated with social deprivation and violence. We describe the prevalence and risk factors for depression during pregnancy, in particular the association with poverty and violence, in a Brazilian setting.

Method. A cross-sectional survey of women in the third trimester of pregnancy attending a public hospital maternity clinic from August 2003 to July 2004 in Rio de Janeiro. Participants were interviewed about their sociodemographic status, obstetric and medical conditions, substance use, stressful life events, and social support. Depression was diagnosed through the Composite International Diagnostic Interview (CIDI).

Results. A total of 230 of 240 eligible women consented to participate. The 12-month prevalence of depression was 19·1% (95% CI 14·4–24·9). On multivariate analyses, having been educated beyond primary school was protective (OR 0·5, 95% CI 0·2–0·9). Risk factors were: being divorced or widowed (OR 4·9, 95% CI 1·3–18·3); a history of depression before pregnancy (OR 7·9, 95% CI 3·1–20·5); loss of an intimate relationship (OR 8·4, 95% CI 3·3–21·4), experienced financial difficulties (OR 6·6, 95% CI 2·5–17·2) and having been exposed to violence in the previous year (OR 4·2, 95% CI 1·5–11·8).

Conclusions. Depression is common during pregnancy and is associated with indicators of socio-economic deprivation, violence and the loss of an intimate relationship, and with a previous history of depression. Psychosocial interventions and appropriate social policies need to be implemented in this population to reduce the burden of maternal depression.

Background. Suicide rates are higher in certain educational groups. The highest rates are generally found in the medical and allied professions, but the empirical evidence for high suicide rates may be questionable. This study compares the rate of suicide among trained physicians, dentists, nurses, police officers and theologians with the rate among other university graduates and the general population according to sex, age and time period.

Method. Census data from 1960, 1970, 1980 and 1990 relating to education were linked to suicide as cause of death data from Statistics Norway, and followed up for the period 1960–2000, comprising 46 and 49 million person-years among men and women respectively.

Results. Physicians still have a higher rate compared with other graduates and the general population, both among males [43·0, 95% confidence interval (CI) 35·3–52·5] and females (26·1, 95% CI 15·1–44·9). Suicide rates increased steeply by age among physicians and other graduates, whereas for non-graduates the rate was highest in the 40–60 years age group. The suicide rate among female nurses was also elevated, whereas police officers seemed to have an intermediate suicide risk. The rate among theologians was low (7·0, 95% CI 2·9–16·9). The suicide rates in the 1990s were significantly lower than in the 1980s.

Conclusions. The high suicide rates among physicians and elderly graduates are of concern. The reasons why graduates are more vulnerable than others when getting older and the low rate among theologians warrant further study.

Background. Numerous nosological decisions are made when moving from the common human symptom of unusual fatigue to the rare chronic fatigue syndrome (CFS). These decisions have infrequently been subjected to rigorous evaluation.

Method. We obtained telephone interview data on fatiguing symptoms from 31406 individuals twins in the Swedish Twin Registry aged 42–64 years; 5330 subjects who endorsed fatigue and possessed no exclusionary condition formed the analytic group. We evaluated the definition and classification of CFS-like illness using graphical methods, regression models, and latent class analysis.

Results. Our results raise fundamental questions about the 1994 Centers for Disease Control criteria as (1) there was no empirical support for the requirement of four of eight cardinal CFS symptoms; (2) these eight symptoms were not equivalent in their capacity to predict fatigue; and (3) no combination of symptoms was markedly more heritable. Critically, latent class analysis identified a syndrome strongly resembling CFS-like illness.

Conclusions. Our data are consistent with the ‘existence’ of CFS-like illness although the dominant nosological approach captures population-level variation poorly. We suggest that studying a more parsimonious case definition – impairing chronic fatigue not due to a known cause – would represent a way forward.

Background. To establish whether high-functioning children with autism spectrum disorder (ASD) have enlarged brains in later childhood, and if so, whether this enlargement is confined to the gray and/or to the white matter and whether it is global or more prominent in specific brain regions.

Method. Brain MRI scans were acquired from 21 medication-naive, high-functioning children with ASD between 7 and 15 years of age and 21 comparison subjects matched for gender, age, IQ, height, weight, handedness, and parental education, but not pubertal status.

Results. Patients showed a significant increase of 6% in intracranium, total brain, cerebral gray matter, cerebellum, and of more than 40% in lateral and third ventricles compared to controls. The cortical gray-matter volume was evenly affected in all lobes. After correction for brain volume, ventricular volumes remained significantly larger in patients.

Conclusions. High-functioning children with ASD showed a global increase in gray-matter, but not white-matter and cerebellar volume, proportional to the increase in brain volume, and a disproportional increase in ventricular volumes, still present after correction for brain volume. Advanced pubertal development in the patients compared to the age-matched controls may have contributed to the findings reported in the present study.

Background. Functional MRI studies have begun to identify neural networks implicated in visuospatial working memory in healthy volunteers and patients with schizophrenia. The study of schizotypal personality disorder (SPD) provides regional analysis in unmedicated patients in the schizophrenia spectrum.

Method. Unmedicated patients with SPD by DSM-IV criteria and normal controls were assessed with fMRI while performing a visuospatial working-memory task. It required the subjects to retain the location of three dots located on the circumference of an imaginary circle and then respond to a query display in which one dot was presented and the subject required to press a button to indicate whether the probe dot location was previously displayed. Subject groups did not differ significantly in spatial memory scores. The exact Talairach and Tournoux coordinates of brain areas previously reported to show activation with spatial memory tasks were assessed.

Results. The majority of these locations showed BOLD response activation significantly less in patients during the memory retention period, including the left ventral prefrontal cortex, superior frontal gyrus, intraparietal cortex and posterior inferior gyrus. Regions in the right middle prefrontal and prestriate cortex showed greater activation at a trend level for patients with SPD than for normal controls. In addition, we replicated the findings of increased activation with the task in healthy volunteers in the premotor areas, ventral prefrontal cortex and parietal cortex.

Conclusions. SPD patients show decreased activation compared to healthy volunteers in key frontal regions and we also provided a partial replication of findings reported in healthy subjects.

Background. Suicidal behaviour and completed suicide are serious problems within British prisons, leading to significant morbidity and mortality, and are the focus of major efforts towards their prevention.

Aim. To explore the demographic, social and psychiatric correlates of suicidal behaviour in prisons in England and Wales and their relationship with health service use; and to develop a combined psychosocial model of risk.

Method. This report analyses the prevalence of suicidal ideation and suicide attempts in the ONS National Prison Survey, and their association with the presence of psychiatric disorders, personality disorder, substance abuse and social risk factors. These data were compared with data from the second national survey of psychiatric morbidity in adults living at home. In both surveys, a two-phase interviewing procedure was used, covering general health, health service use, assessment of psychiatric disorders, life events, social supports, suicidal behaviour, activities of daily living, sociodemographic data, substance abuse and intelligence.

Results. Suicidal thoughts and suicide attempts were commoner in prisons than in the general population and these were significantly associated with higher rates of psychosis, neurosis and personality disorder in prisons. In addition, demographic and factors such as being young, single, white, leaving school early and experiencing poor social support and significant social adversity were important risk factors for suicidal thoughts. Crucially, there was no separate category of people at suicidal risk who did not have psychiatric disorders.

Conclusions. The high rates of suicidal behaviour in prisons cannot be addressed without adequate attention to the high rates of psychiatric disorder and vulnerability factors in prisoners.

Background. Empirical findings suggest that psychiatric illness is associated with cardiovascular disease (CVD). The purpose of this study was to compare the strength of the association of lifetime post-traumatic stress disorder (PTSD) and lifetime major depression on CVD among Northern Plains American Indians.

Method. A total of 1414 participants aged 18–57 years completed a structured interview that assessed psychiatric diagnoses, alcohol abuse/dependence, self-reported CVD, and traditional CVD risk factors including age, sex, education, diabetes, high blood pressure, and smoking. Logistic regression analyses compared the odds ratios of CVD in participants with and without diagnosed PTSD or major depression.

Results. The rates of lifetime PTSD and major depression were 15% and 8% respectively. CVD was more commonly reported by participants with PTSD than by those without PTSD (12% v. 5%, p[les ]0·01). Likewise, more participants with major depression reported CVD than did their non-depressed counterparts (14% v. 6%, p[les ]0·05). PTSD was significantly associated with CVD even after controlling for traditional CVD risk factors and major depression (odds ratio 2·0, confidence interval 1·1–3·8). In contrast, the association of major depression with CVD was not significant after accounting for both traditional risk factors and PTSD.

Conclusions. Rates of PTSD are high in American Indian communities. Rising CVD rates in this population may be better understood if PTSD is considered along with other traditional risk factors. Future research should examine the association and mechanisms of PTSD and CVD prospectively. Such data could lead to more effective CVD prevention efforts for American Indians.

Background. Nicotine withdrawal is associated with failed smoking cessation and thus contributes to continuance of the habit and increases risk of smoking-related illnesses. Withdrawal is also associated with psychiatric disorders such as depression and alcoholism. However, relatively little is known about how to characterize the severity of withdrawal, including whether withdrawal subtypes exist in male smokers. If so, do these subtypes represent quantitative or qualitative differences?

Method. Smoking and withdrawal data were obtained from 4112 male–male twin pairs of the Vietnam Era Twin Registry during a 1992 administration of the Diagnostic Interview Schedule. Latent Class Analysis (LCA) was used to derive significantly different nicotine withdrawal profiles, and their association with psychiatric disorders was assessed. Genetic and environmental contributions and the correlation between these contributions were evaluated using bivariate biometrical modeling of the withdrawal phenotype and failed smoking cessation.

Results. The LCA model which best fit the data was a four-class severity continuum. Psychiatric disorders were significantly associated with more severe classes and the magnitude of the association increased as withdrawal severity increased. Genetics accounted for 31% and 51% of the variance in risk for withdrawal and failed cessation, respectively. The genetic contributions were significantly correlated (r=0·37).

Conclusions. Nicotine withdrawal classes are characterized by quantitative differences. The strong association between psychiatric disorders and withdrawal severity and the significant genetic correlation between withdrawal and cessation highlight the importance of withdrawal severity. Further refinement of the DSM definition of withdrawal to incorporate severity ratings may be warranted.

Background. We prospectively studied outcomes of sex reassignment, potential differences between subgroups of transsexuals, and predictors of treatment course and outcome.

Method. Altogether 325 consecutive adolescent and adult applicants for sex reassignment participated: 222 started hormone treatment, 103 did not; 188 completed and 34 dropped out of treatment. Only data of the 162 adults were used to evaluate treatment. Results between subgroups were compared to determine post-operative differences. Adults and adolescents were included to study predictors of treatment course and outcome. Results were statistically analysed with logistic regression and multiple linear regression analyses.

Results. After treatment the group was no longer gender dysphoric. The vast majority functioned quite well psychologically, socially and sexually. Two non-homosexual male-to-female transsexuals expressed regrets. Post-operatively, female-to-male and homosexual transsexuals functioned better in many respects than male-to-female and non-homosexual transsexuals. Eligibility for treatment was largely based upon gender dysphoria, psychological stability, and physical appearance. Male-to-female transsexuals with more psychopathology and cross-gender symptoms in childhood, yet less gender dysphoria at application, were more likely to drop out prematurely. Non-homosexual applicants with much psychopathology and body dissatisfaction reported the worst post-operative outcomes.

Conclusions. The results substantiate previous conclusions that sex reassignment is effective. Still, clinicians need to be alert for non-homosexual male-to-females with unfavourable psychological functioning and physical appearance and inconsistent gender dysphoria reports, as these are risk factors for dropping out and poor post-operative results. If they are considered eligible, they may require additional therapeutic guidance during or even after treatment.

Background. Acts of suicide differ widely in the amount of planning preceding the act. Correlates of completed suicide in China identified in a previous investigation were re-examined to identify those that may be especially relevant to low-planned (impulsive) and high-planned suicidal behavior. The association of planning and method in completed suicide was also assessed.

Method. A psychological autopsy study of 505 suicide decedents aged [ges ]18 years sampled to be representative of suicides in China was conducted. Multinomial regression analyses compared three levels of suicide planning (low, intermediate, high).

Results. Women and younger individuals were more likely to carry out low-planned and intermediate-planned than high-planned acts of suicide. Greater acute stress distinguished low-planned from high-planned suicides. Ingestion of pesticides stored in the home was a more commonly employed method in low-planned than high-planned suicides.

Conclusions. Low-planned suicides are more common in women, in younger individuals, and among those who are experiencing acute stress. Prevention strategies targeted at restricting access to pesticides may preferentially lower the rate of low-planned suicides.

Background. There are significant barriers to accessing effective psychological therapy in primary care resulting from a lack of suitably trained therapists to meet current demand. More efficient service delivery using minimal interventions (such as bibliotherapy) provided by paraprofessional therapists may be one method of overcoming these problems, and is the subject of attention in the UK and elsewhere. A randomized trial was conducted to test the clinical effectiveness of this model. Assistant psychologists delivered a guided self-help intervention to patients with anxiety and depression who were currently waiting for psychological therapy.

Method. A total of 114 patients were randomized either to guided self-help or a waiting-list control group. All patients were followed up 3 months later, prior to starting conventional psychological therapy. Measures included self-reported adherence to the intervention, anxiety and depressive symptoms, social functioning and patient satisfaction.

Results. Adherence to the guided self-help intervention was acceptable and patients reported satisfaction with the intervention. However, there were no statistically significant differences between groups in anxiety and depression symptoms at 3 months.

Conclusions. The results demonstrate that this model of guided self-help did not provide additional benefit to patients on a waiting list for psychological therapy. The results are considered in the context of possible internal and external validity threats, and compared with previous trials of minimal interventions. The implications of the results for the design of future minimal interventions are considered.

Background. Offspring of depressed parents experience impairment in a number of domains of functioning. Few studies have examined the impact of both maternal and paternal depression and co-morbid psychopathology on offspring functioning.

Method. Oregon Adolescent Depression Project participants were administered diagnostic interviews and completed measures of psychosocial functioning during adolescence (mean=16·6, S.D.=1·19) and again during young adulthood (mean=24·5, S.D.=0·51). Diagnostic interviews were also conducted with the mothers and fathers of the target individual.

Results. After controlling for relevant demographic characteristics, parental co-morbid psychopathology, and offspring psychopathology, maternal depression was associated with higher levels of physical symptoms (β=0·14, S.E.=0·07) during adolescence, and higher levels of minor stressors (β=2·52, S.E.=1·07) and a greater risk for using mental health services (OR 1·86, 95% CI 1·14–3·03) in young adulthood. Paternal depression was associated with offspring experiencing more major stressors (β=0·27, S.E.=0·07), having lower perceived social competence (β=−0·17, S.E.=0·08), and being more likely to attempt suicide (OR 2·65, 95% CI 1·19–5·92) during adolescence, as well as lower perceived social competence (β=−1·21, S.E.=0·49) in young adulthood.

Conclusions. Offspring of depressed parents demonstrate impairment in a variety of domains, even after controlling for the effects of their own psychopathology. Further research on the mechanisms that lead to these impairments, as well as the role of these impairments in the subsequent development of psychopathology, is warranted.

Background.Randomized clinical trials indicate a benefit from combining medications with cognitive behavioral therapy (CBT) relative to medication alone for panic disorder. Using an as-treated analysis, we evaluated whether the addition of CBT enhanced outcomes for panic disorder relative to medications alone in the primary-care setting.

Method.Primary-care patients with panic disorder reported on their receipt of CBT and medications over the 3 months following baseline assessment. The degree to which outcomes for those who used anti-panic medications were enhanced by the receipt of at least one component of CBT was analyzed using a propensity score model that took into account observable baseline patient characteristics influencing both treatment selection and outcomes.

Results.The addition of CBT resulted in statistically and clinically significant improvements at 3 months on anxiety sensitivity, social avoidance, and disability. Also, patients receiving CBT in the first 3 months of the study were more improved at 12 months than patients who took medications only during the first 3 months of the study.

Conclusions.The clinical utility of the findings are discussed in terms of the importance of primary-care physicians encouraging their panic disorder patients to receive CBT as well as medications.

Background. The objectives of the study were to examine linkages between exposure to childhood abuse and interparental violence and the subsequent development of panic attacks and panic disorder using data gathered on a birth cohort of 1265 New Zealand young people studied to the age of 21 years.

Method. Data on: (a) exposure to child abuse and interparental violence; (b) the development of panic attacks and panic disorder; and (c) other childhood and related factors were gathered over the course of a 21-year longitudinal study.

Results. After adjustment for childhood and related factors, exposure to childhood physical abuse was associated with a significantly increased risk of later panic attack (OR 2·3, 95% CI 1·1–4·9) and panic disorder (OR 3·0, 95% CI 1·1–7·9); childhood sexual abuse was associated with a significantly increased risk of panic attack (OR 4·1, 95% CI 2·3–7·2) and a marginally significant increase risk of panic disorder (OR 2·2; 95% CI 0·98–5·0). Exposure to interparental violence was unrelated to later panic attack or disorder after adjustment.

Conclusions. Exposure to childhood sexual and physical abuse was associated with increased risks of later panic attack/disorder even after adjustment for prospectively assessed confounding factors. However, exposure to interparental violence during childhood was not related to increased risk of later panic attack/disorder after adjustment. These data suggest the need for clinicians to be aware that patients with histories of childhood physical and sexual abuse may be at increased risk for panic during young adulthood.

Background. There is increasing evidence that attitudes and beliefs are important in predicting adherence to treatment and medication in depressive and bipolar disorders. However, these attitudes have received little study in patients whose disorders were sufficiently severe to require hospitalization.

Method. The Antidepressant Compliance Questionnaire (ADCQ) was mailed to a large population of patients with depressive or bipolar disorder, representative of patients treated in hospital settings in Denmark.

Results. Of the 1005 recipients, 49·9% responded to the letter. A large proportion of the patients (40–80%) had erroneous views as to the effect of antidepressants. Older patients (over 40 years of age) consistently had a more negative view of the doctor-patient relationship, more erroneous ideas concerning the effect of antidepressants and a more negative view of antidepressants in general. Moreover, their partners agreed on these negative views. Women had a more negative view of the doctor-patient relationship than men, and patients with a depressive disorder had a more negative view of antidepressants than patients with bipolar disorder. The number of psychiatric hospitalizations or the type of treating physician (general practitioner, psychiatrist in private practice, community psychiatrist, hospital psychiatrist, other doctor) did not affect attitudes and beliefs.

Conclusion. Lack of knowledge about affective disorder and its treatment and a critical attitude, especially among older patients, may add to an adverse prognosis of depressive and bipolar disorders.

Background. In patients with chronic medical conditions, depression can be viewed as an expected reaction to illness or an independent condition requiring active treatment. We examine how clinical and functional outcomes of depression treatment compare in primary-care patients with and without chronic medical illness.

Method. Health plan administrative data were used to identify primary-care patients initiating antidepressant treatment, including a general sample (n=204) and cohorts with ischemic heart disease (n=68), diabetes (n=93), or obstructive lung disease (n=74). Telephone interviews at baseline, 2 months, and 6 months assessed depression (Structured Clinical Interview for DSM-IV, Hopkins Symptom Checklist depression scale), functional status (SF-36) and days of disability because of to illness.

Results. At baseline, depression severity in patients with diabetes and obstructive lung disease was similar to those without medical co-morbidity, but significantly lower in those with ischemic heart disease. Social and emotional functioning were similar across all groups, but those with chronic medical illness reported greater physical impairment. All groups showed significant improvement in depression over six months, but the rate of improvement was significantly slower in those with heart disease. All groups showed significant and similar improvement in social and emotional functioning, but physical functioning showed little change. Days of disability and restricted activity improved significantly in all groups. Improvement in depression during treatment was strongly related to change in disability.

Conclusions. Patients with chronic medical illness and co-morbid depression show significant improvements in mood, social and emotional functioning, and disability following initiation of depression treatment. Depression may be a stronger determinant of disability than is stable chronic medical illness.

Background. Cognitive performance was compared in the genetically and neurobiologically related disorders of Tourette's syndrome (TS) and obsessive–compulsive disorder (OCD), in three domains of executive function: planning, decision-making and inhibitory response control.

Method. Twenty TS patients, twenty OCD patients and a group of age- and IQ-matched normal controls completed psychometric and computerized cognitive tests and psychiatric rating scales. The cognitive tests were well-characterized in terms of their sensitivity to other fronto-striatal disorders, and included pattern and spatial recognition memory, attentional set-shifting, and a Go/No-go set-shifting task, planning, and decision-making.

Results. Compared to controls, OCD patients showed selective deficits in pattern recognition memory and slower responding in both pattern and spatial recognition, impaired extra-dimensional shifting on the set-shifting test and impaired reversal of response set on the Go/No-go test. In contrast, TS patients were impaired in spatial recognition memory, extra-dimensional set-shifting, and decision-making. Neither group was impaired in planning. Direct comparisons between the TS and OCD groups revealed significantly different greater deficits for recognition memory latency and Go/No-go reversal for the OCD group, and quality of decision-making for the TS group.

Conclusions. TS and OCD show both differences (recognition memory, decision-making) and similarities (set-shifting) in selective profiles of cognitive function. Specific set-shifting deficits in the OCD group contrasted with their intact performance on other tests of executive function, such as planning and decision-making, and suggested only limited involvement of frontal lobe dysfunction, possibly consistent with OCD symptomatology.

Background. Serotonin is a good candidate for major depression. We attempted to replicate the study by Caspi and colleagues [Science (2003) 301, 386–389] which reported a significant interaction between serotonin transporter (5-HTTLPR) genotype and stressful life events when predicting major depression.

Method. We typed the serotonin promoter 5-HTTLPR gene in 1206 male and female twins aged 19–78 years (mean=39, S.D.=11). A DSM-IV diagnosis of major depression was available for 1199 twins. Most of these twins had participated in a 1988–1990 study which included a stressful life events inventory and self-report measure of depression based on the SCL-90 and DSSI/sAD. Complete 5-HTT genotype and life events data, self-report symptoms and major depression diagnoses were available for 1091 subjects. We regressed categorical and ordinal measures of depression onto stressful life events and genotype.

Results. There were significant main effects for stressful life events but there was no evidence for any effect of 5-HTT genotype, nor a genotype×stressful life event interaction.

Conclusions. Regardless of whether our results were based on binary logistic or ordinal regression analyses we found no evidence to support a main effect of 5-HTTLPR, or an interaction between the 5-HTTLPR genotype and stressful life events on major depression. Only 20% of our subjects were aged below 30 years. It is possible that the effect reported by Caspi and colleagues is specific to young people, in which case our study has much less power in this age group.

Background. The prevalence of use of many psychoactive substances has changed considerably in recent years. While genetic factors impact on overall risk for substance use, we know little about whether the etiological importance of these factors differs across birth cohorts. One theory, which postulates that heritability of deviant traits increases in permissive environments, predicts a positive relationship across cohorts between prevalence and heritability of substance use.

Method. The lifetime history of use of tobacco, cannabis, cocaine, sedatives and stimulants were assessed in 4826 twins from male–male and female–female pairs born in Virginia from 1934 to 1974. Using empirical methods based on prevalence by birth year, these twins were divided into three cohorts for each substance (e.g. for cannabis 1934–1953, 1954–1968 and 1969–1974). Structural equation modeling was performed using the Mx software package.

Results. Prevalence rates for psychoactive substance use differed substantially across cohorts, most markedly for cocaine, sedatives and stimulants, which were highest in the 1958–1963 cohort. However, for all substances, the best-fit model constrained estimates of the etiological role of genetic and environmental risk factors to be equal across both sex and cohort.

Conclusions. We found no evidence in this sample for any systematic relationship between heritability and prevalence of psychoactive substance use – which should be a rough index of drug availability and/or acceptability. This sample had reasonable power to detect large changes in heritability across cohorts and at least moderate power to detect relatively small changes.