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Family members are known to serve as geographical attractors in migration, yet evidence for sex‐biased family migration in developed societies is mixed. We investigate gender differences in migration of family members in Finland. Using the FinnFamily register data set (N = 60,000 index individuals and their close kin), we explore family coresidence and migration within the 19 administrative regions of Finland in 1970–2012. We study the propensity for regional migration by gender and age, the likelihood for children to reside in the same region as their parents and to reunite after migration to different regions, and whether siblings function as regional attractors. Finland experienced intense regional migration to the capital area during the study period. Individual migration propensity peaked at infancy and at 18–28 years. Throughout their lives, most Finns live in the same region as their family members: over 65% with parents, over 55% with full sibling(s), and over 50% with half sibling(s). Siblings are likely to migrate to the same region, and having more siblings strengthens this attraction. Results also indicate some degree of patrilocality. Daughters migrate earlier and with higher rates than sons, whereas sons are at any age more likely to live in the same region as their parents. The propensity for adult brothers to live in the same region is also higher than for other sibling pairs. Family members serve as important geographical attractors to each other through the life course in contemporary Finland, and this is more pronounced for males than for females.

Studies have suggested both adverse and protective associations of obesity with depressive symptoms. We examined the contribution of environmental and heritable factors in this association. Participants were same-sex twin pairs from two population-based twin cohort studies, the Older Finnish Twin Cohort (n = 8,215; mean age = 44.1) and the US Midlife Development in the United States (MIDUS; n = 1,105; mean age = 45.1). Body mass index (BMI) was calculated from self-reported height and weight. Depressive symptoms were assessed using Beck's Depression Inventory (BDI; Finnish Twin Cohort), and by negative and positive affect scales (MIDUS). In the Finnish Twin Cohort, higher BMI was associated with higher depressive symptoms in monozygotic (MZ) twins (B = 2.01, 95% CI = 1.0, 3.0) and dizygotic (DZ) twins (B = 1.17, 0.5, 1.9) with BMI >22. This association was observed in within-pair analysis in DZ twins (B = 1.47, CI = 0.4, 2.6) but not in within-pair analysis of MZ twins (B = 0.03, CI = -1.9, 2.0). Consistent with the latter result, a bivariate genetic model indicated that the association between higher BMI and higher depressive symptoms was largely mediated by genetic factors. The results of twin-pair analysis and bivariate genetic model were replicated in the MIDUS sample. These findings suggest an association between obesity and higher depressive symptoms, which is largely explained by shared heritable biological mechanisms.

Studies on personality and friendship have often focused on similarities between friends, while differences in friendship patterns have received less attention. We used data from the British Household Panel Survey data (N=12,098) to investigate how people's personalities are related to various characteristics of their three closest friends. All personality traits of the Five Factor Model were associated with several friendship characteristics with effect sizes corresponding to correlations from r =-.06 to r = .09. Openness was an especially prominent and idiosyncratic trait; individuals with high openness were more likely to have friends who live further away, are of the opposite sex and another ethnicity, and whom they meet less often. Agreeableness, and to some extent extraversion, were related to more traditional friendship ties. Thus individuals with high agreeableness had known their friends for a longer time, lived close to them, and had more stay-at home people and kin among their friends. We conclude that personality is relevant for the social patterning of close friendship relations.

Personality affects dyadic relations and teamwork, yet its role among groups of friends has been little explored. We examine for the first time whether similarity in personality enhances the effectiveness of real-life friendship groups. Using data from a longitudinal study of a European fraternity (10 male and 15 female groups), we investigate how individual Big Five personality traits were associated with group formation and whether personality homophily related to how successful the groups were over 1 year (N = 147-196). Group success was measured as group performance/identification (adoption of group markers) and as group bonding (using the inclusion-of-other-in-self scale). Results show that individuals' similarity in neuroticism and conscientiousness predicted group formation. Furthermore, personality similarity was associated with group success, even after controlling for individual's own personality. Especially higher group-level similarity in conscientiousness was associated with group performance, and with bonding in male groups.

Birth intervals are known to influence child and parental health and wellbeing, yet studies on the recent development of birth intervals in contemporary developed societies are scarce. We used individual-level representative register data from Finland (N=26,120; 54% women) to study the first interbirth interval of singleton births in cohorts born in 1955, 1960, 1965, 1970, and 1975. In women, the average interbirth interval has shortened by 7.8 months and in men by 6.2 months between the cohorts of 1955 and 1975. A higher age at first birth was associated with shorter birth intervals (in women, b = -1.68, p<.001; in men, b = -1.77, p<.001 months per year). Educational level moderated the effect of age at first on the first birth interval in both sexes. Due to rising ages at first birth in developed societies and the manifold ramifications of shorter birth intervals, this topic deserves more scholarly attention and studies from other countries.