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The aim of the study was to investigate the relationship between the Flynn effect and the effects of age differences between siblings on the intelligence difference between them. In Norway, the secular trends in intelligence-test score means vary both in magnitude and direction. We identified three periods: one period where the mean intelligence increased across birth cohorts (1950-1956), one period where the means decreased (1976-1983), and one period with no appreciable Flynn effect (1960-1965). In a data base comprising birth year and intelligence data on more than 900,000 males meeting at mandatory conscription between their 18th and 21st birthday, we identified more than 69,000 brother pairs where both brothers had been born in exactly one of the periods mentioned above. In this study group the relationship between age differences between brothers and the intelligence difference could be studied. The results showed that in the period with increasing intelligence means across cohorts, the intelligence difference between brothers decreased with increasing age differences. In the period with decreasing means, the difference between the later-born and the earlier-born brother increased across age differences. No systematic effects of age difference on mean intelligence differences were found in the period without a Flynn effect. Regression analyses showed that the Flynn effect can be quite well predicted from the effects of the age differences between brothers on their intelligence-test scores. We conclude that the factors causing the Flynn effect also work within sibships. Hypotheses positing that the Flynn effect is solely caused by between-families factors (e.g. the heterosis hypothesis) are weakened. The present results also entail that the birth order effect observed in Norway is in part conditional on the Flynn effect. (Contains 3 figures and 1 table.)

Background Some previous studies indicate that parental hearing loss may have negative consequences in the parent–child relationship. However, most of these studies are qualitative or have apparent methodological shortcomings. Objective This study is the first of its kind conducted in a large population-based sample with audiometrically measured hearing loss aimed at investigating the extent to which parental hearing loss affects adolescents' mental health. Methods Questionnaires were administered to the adult (>19 years) and adolescent (age 13–19 years) population of Nord-Trøndelag county, Norway (1995–97), which collected information on mental and somatic health, including hearing loss. For adults participating in the study, pure tone audiometry tests were also administered. In total, 4047 fathers and 4785 mothers with self-reported hearing loss data were identified. The corresponding numbers with measured hearing loss data included 4079 fathers and 4861 mothers. The associations between the degrees of self-reported or measured parental hearing loss and the mental health of their adolescent, measured by Hopkins Symptom Check List (SCL) 5, were estimated using generalized estimating equations. After adjusting for several covariates, the mental health symptoms of adolescents were compared by parental hearing loss (i.e., with versus without hearing loss). Results Adolescents whose mothers had severe measured or self-reported hearing loss had significantly worse mental health than their counterparts whose mothers did not have a hearing loss. No corresponding effects were found in the adolescents whose mothers had only a slight/moderate hearing loss, neither measured nor self-reported. Paternal slight/moderate self-reported hearing loss was associated with a small significant reduction of mental health in the adolescents, although attenuated when adjusting for paternal distress. No significant effects were detected in the adolescents whose fathers had measured hearing loss. Conclusion Severe maternal hearing loss is associated with significantly increased adolescent distress. [ABSTRACT FROM AUTHOR]

Background: The association between mental distress and divorce is well established in the literature. Explanations are commonly classified within two different frameworks; social selection (mentally distressed people are selected out of marriage) and social causation (divorce causes mental distress). Despite a relatively large body of literature on this subject, selection effects are somewhat less studied, and research based on data from both spouses is scarce. The purpose of the present study is to investigate selection effects both at the individual level and the couple level. Methods: The current study is based on couple-level data from a Norwegian representative sample including 20,233 couples. Long-term selection effects were tested for by means of Cox proportional hazard models, using mental distress in both partners at baseline as predictors of divorce the next 16 years. Three identical sets of analyses were run. The first included the total sample, whereas the second and third excluded couples who divorced within the first 4 or 8 years after baseline, respectively. An interaction term between mental distress in husband and in wife was specified and tested. Results: Hazard of divorce was significantly higher in couples with one mentally distressed partner than in couples with no mental distress in all analyses. There was also a significant interaction effect showing that the hazard of divorce for couples with two mentally distressed partners was higher than for couples with one mentally distressed partner, but lower than what could be expected from the combined main effects of two mentally distressed partners. Conclusions: Our results suggest that mentally distressed individuals are selected out of marriage. We also found support for a couple-level effect in which spouse similarity in mental distress to a certain degree seems to protect against divorce. [ABSTRACT FROM AUTHOR]