A number of studies have documented significant gains in mean IQ scores across generations (the Flynn effect). Flynn effects have been found in more than 30 industrialized nations, including Norway, but also in developing nations in Latin America and Africa. In the current paper, we present international and Norwegian results attained from young male military conscripts, encompassing new and unpublished data. In accordance with international data, the mean IQ scores in Norway increased from test years in the late 1950s (birth cohorts ≈ 1938–1940), but with decreasing gain rates, to the mid-1990s. After the mid-1990s, increases in the means ceased and exhibited decreasing tendencies. Our new data set shows that these decreases have continued into the new millennium. Practical and methodological consequences of the secular trends in IQ scores are often overlooked. We address issues related to the use of intelligence tests in situations where decisions with potentially serious consequences for participants are involved. In particular, we underscore the need for test norms that take the Flynn effect into consideration. In cross-sectional studies, age and birth cohort are completely confounded. Effects of birth cohort on intelligence (Flynn effect) have often been wrongly interpreted as age effects. To study age effects, longitudinal studies are needed. There are several theories addressing the possible causes of the Flynn effect. In the present paper we discuss how well existing theories explain known facts, with special emphasis placed on the Norwegian data.

We examine a sample of Norwegian twin conscripts for evidence of an interaction between parental education and the heritability of general cognitive ability (GA). Ability scores were obtained on 1706 pairs of twins who were conscripted into the Norwegian Armed Forces between 1931and 1960. Education scores were available for mothers and fathers; the majority of the parents had less than a high school education. GA scores were heteroscadistic with respect to mid-parent education, with reduced variability at higher levels of education. Both MZ and DZ twin correlations for GA were linearly and negatively related to mid-parent education, DZ twins substantially more so. When the model was extended to an ACE model consisting of standardized positive ACE variance components, the modification appeared to disappear. Further analysis revealed that this occurred because the steep decline of DZ twin correlations with increasing mid-parent education resulted in a violation of the classical twin model for much of the parameter space. Other phenomena that might result in large declines in DZ twin correlations are considered, along with implications for other studies of socioeconomic interactions with the heritability of GA in European samples.

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.

Objective The aim of this birth cohort study was to determine the relationship between birth weight and the risk of overweight in young adulthood. Methods: Data from the Medical Birth Registry of Norway were linked with register data from the National Conscript Service. This study used data on the 348,800 males who were born at term in single births in Norway during 1967 to 1984, and who were examined at the mandatory military conscription (98% were examined the year they turned 18 or 19 years of age). Sibling comparisons were conducted in the 11,865 sibships of two or more full brothers in which at least one brother was overweight (body mass index ≥25.0 kg/m 2 ) and at least one brother was not overweight. Results: When all the men in the study population were compared with each other there was a “J”‐shaped association between birth weight and the adjusted odds of overweight. When the men were compared with their brothers, the adjusted odds of overweight increased in an exponential way (linearly in logit) over the entire range of the birth weight scale. A within‐family difference of 100 g in birth weight was associated with a within‐family difference of 3.5% (99% confidence interval: 2.5–4.6) in the odds of overweight. Conclusions: There is a positive within‐family association between birth weight and the odds of overweight in young Norwegian men born at term. Am. J. Hum. Biol. 27:564–569, 2015. © 2015 Wiley Periodicals, Inc.

Background: Studies of caregiver burden and somatic illness tend to be based on relatively small, clinical samples. Longitudinal, population based studies on this topic are still scarce and little is known about the long-term impact of partner illness on spousal mental health in the general population. In this study we investigate whether spouses of partners who either have become somatically ill or cured from illness in an 11 year period - or who have long-term illness - have different mental health scores compared to spouses of healthy partners.Methods: Approximately 9000 couples with valid self-report data on a Global Mental Health (GMH) scale and somatic illness status were identified. The diagnoses stroke, angina pectoris, myocardial infarction and severe physical disability, were transformed into a dichotomous 'any illness'-scale, and also investigated separately. Analyses of variance (ANOVA) stratified by sex were conducted with spousal GMH score at follow-up (1995-97, T2) as the outcome variable, adjusting for spousal GMH score at baseline (1984-86, T1) and several covariates.Results: Results showed that male and female spouses whose partners had become somatically ill since T1 had significantly poorer mental health than partners in the reference category, comprising couples healthy at both time points. Further, female spouses of partners who had recovered from illness since T1 had significantly better mental health than controls. Of the somatic conditions, physical disability had the most significant contribution on spousal GMH, for both sexes, in addition to stroke on male spouses' GMH. The effect sizes were small. Some of the loss of spousal mental health seems to be mediated by the ill persons' psychological distress.Conclusion: The occurrence of partner illness during the follow-up period affect the mental health of spouses negatively, while partner recovery appeared to be associated with improved mental health scores for female spouses. Of the measured conditions, physical disability had the largest impact on spousal distress, but for some conditions the distress of the ill person mediated much of the loss of mental health among spouses.

In the present paper published data and new analyses are presented and discussed in order to demonstrate the power of family data (siblings and parents to military conscripts with IQ data) in the study of the Flynn effect (FE). In particular, it is shown how studies of the mean intelligence changes in sibships of different sizes and changing proportions of sibship sizes can enhance our understanding how these factors may influence FE. Some new analyses of correlations between intelligence and sibship sizes illustrate how family data can be used to investigate changes in the correlation pattern across generations. It is shown that comparison of the secular trends in the general population and in sibling pairs can be a powerful method in the exploration of the relative influence of between-families and within-families factors in the FE. Surprising connections between the birth order effect on intelligence and the FE are demonstrated.

The current study examined the relationship between early interaction, parenting stress, maternal psychological distress symptoms, and behavior problems and health-related quality of life among children born to mothers in opioid maintenance treatment (OMT) in Norway during the period 2005–2007 (N = 36). This group was compared with a normative sample of mothers without substance abuse problems and their children (N = 36). There were significant group differences (p < .01) in perceived child problems in toddlerhood. In a regression model, mothers' self-reported psychological distress symptoms in terms of depression and anxiety symptoms significantly predicted child behavior problems (p < .01) and health-related quality of life (p < .01) rather than parenting stress. No significant, unique effect of exposure was found after controlling for other factors that could influence developmental outcomes. These findings add to the growing evidence on the importance of maternal psychological well-being for child development, and underscore the need to address opioid-maintained women's personal maladjustment and the constellation of stress experienced by mothers in recovery.

Aims: To examine whether observed changes in self-reported psychological distress symptoms reflect true changes in psychological distress in the population, or more specifically, to present statistical methods to check for nonresponse bias and demographic changes. Methods: Lack of representativity, nonresponse bias and demographic changes were controlled for by weighing of data (sample-balancing or raking). Results: Controlling for age, gender and education, or holding the demographic structure constant over time, slightly weakened the decrease in psychological distress from 1998 to 2002, and left the changes in psychological distress from 2002 to 2008 almost unchanged. When the level of psychological distress was held constant across years in every subgroup defined by age, gender and education, in order to isolate the effects of changes in demography, the distress scores showed only minor variation across data collection occasions from 1998 to 2008. Conclusions: The observed modest decrease in psychological distress from 1998 to 2002 may partly be explained by selection and demographic changes, while this is not the case with the more pronounced changes from 2002 to 2008.

This study investigated the cross-sectional associations between various somatic conditions in one partner and the level of distress and well-being in the spouse. The study is based on survey data from the Norwegian Nord-Trøndelag Health Study, HUNT II (1995-1997). A sample of 9,797 married or cohabiting couples with valid data on subjective well-being (SWB), psychological distress (Hopkins Symptom Check List (SCL)-10) and somatic illness were identified. Regression analyses stratified by sex were conducted with SCL-10 and SWB scores as dependent variables and a joint somatic score as predictor, including; stroke, cancer, angina, myocardial infarction and physical disability (PD). The contribution of each somatic condition was also explored. Spouses of persons previously diagnosed with at least one somatic condition scored significantly lower on SWB and significantly higher on SCL-10 than spouses of healthy persons, though effect sizes were small. The effect seems to be at least partly mediated by the ill partner's psychological distress. Of the specific conditions, PD had the most significant contribution for both genders, though an association between male angina and spousal distress/SWB was also demonstrated.

A number of studies point to methadone exposure in utero as a possible risk factor in the developing mother–infant relationship in the first year of life. This study is part of a larger, national follow-up of 38 infants prenatally exposed to methadone or buprenorphine and 36 comparison, low-risk infants. The aim of the present paper is to assess the quality of mother–infant relationship when the infants are 6 months old. Videotaped mother–infant interactions were rated in a global scale (NICHD). Maternal and infant contributions collapsed into the variables “infant style” and “maternal style” showed that the only factor making significant contribution to the outcome measure “dyadic mutuality” was maternal style. The importance of group membership (exposed versus non-exposed), was reduced when controlling for maternal drug use prior to opioid maintenance treatment (OMT), maternal depression and parenting stress as well as infants’ developmental status and sensory-integrative functions. This suggests that prediction of dyadic mutuality should be based on individual characteristics rather than group characteristics. These results support previous research findings that methadone and buprenorphine use per se does not have direct influence on the quality of early mother–infant relationship, but tailored follow-up procedures targeting drug-free pregnancies and parenting support are beneficial for women in OMT and their children.

OBJECTIVE:To examine the negative statistical relationship between educational level and risk of anxiety disorders, and to estimate to what extent this relationship may be explained by genes or environmental factors influencing both phenotypes. METHOD:Registry data on educational level for 3339 young adult Norwegian twin pairs and diagnostic data on anxiety disorders for 1385 of these pairs were analysed, specifying structural equations models using MX software. RESULTS:In the best-fitting model, genes accounted for 59% of the variance in education. 18% of the variance was due to environmental factors shared by co-twins, and the remaining 23% due to non-shared environment; 46% of the variance in liability to anxiety disorders was genetic, the remaining variance was due to non-shared environment. A phenotypic polychoric correlation of -0.30 between educational level and 'any anxiety disorder' was estimated to be primarily (83% in the best-fitting model) caused by genes common to the two traits. CONCLUSION:The relationship between low education and risk of anxiety disorders appears to be primarily determined by genetic effect common to educational level and anxiety disorders.

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.

Research on twins and unrelated persons living together indicates that, although differences in intelligence between persons are caused by both genetic and environmental factors, similarities-and especially those between adults-are mostly or exclusively due to shared genes. However, twin and adoption designs have been criticized for incorrectly estimating the effects of the environment on the similarity between relatives, and studies of environmental effects in other family constellations may be enlightening. In a sample comprising more than 334,000 pairs of brothers (ages 18-21 years) who were tested at the mandatory conscription for military service in Norway, correlations between brothers' intelligence-test scores decreased with increasing age difference between the brothers. This result indicates that family environmental factors have an impact on the intelligence of young adults. Analyses of subgroups defined by family size and parental education demonstrated that the effects of age difference are essentially independent of these factors.

The present study investigates the impact of changing fertility patterns on the Flynn effect. Intelligence test data comprised scores of army conscripts on an arithmetic, language and a Raven-similar test, and a composite score (General Ability). Family data of the conscripts enabled a decomposition of the population mean into effects of sibship size on the mean intelligence and the proportion of the persons comprising the various sibship sizes within each of 13 birth cohort groups (each comprising 3 birth years). Both the means within each sibship and the proportions of the different sibship sizes varied across cohorts. Estimated changes in means due to changing proportions of sibship sizes alone were calculated by fixing the mean intelligence test score within the different sibship sizes at the level of the oldest birth cohort (1938–1940) and letting the proportions of the different sibship sizes take their empirical values in each of the subsequent 12 three-year cohort groups. It is concluded that changing proportions of sibship sizes had a moderate effect both on General Ability and the subtest scores, and that most of the changes were connected to changing sibship means across cohorts.

The main aim of this paper was to resolve the correlation between intelligence test scores and standing height into genetic and environmental components. Data on 1181 identical and 1412 fraternal twin pairs (all males) were retrieved by matching files from the Norwegian Army with twin registries. The data were analyzed by means of a structural equation model comprising latent genetic, shared environmental and nonshared environmental factors and correlations between them. A major part of the height--intelligence correlation was due to correlated shared environments (59% of the phenotypic height--intelligence correlation), but statistically significant effects of correlated genes and nonshared environments were also found (respectively 35% and 6% of the phenotypic correlation).

The present paper reports secular trends in the mean scores of a language, mathematics, and a Raven-like test together with a combined general ability (GA) score among Norwegian (male) conscripts tested from the mid 1950s to 2002 (birth cohorts ≈1935–1984). Secular gains in standing height (indicating improved nutrition and health care) were also investigated. Substantial gains in GA were apparent from the mid 1950s (test years) to the end 1960s–early 1970s, followed by a decreasing gain rate and a complete stop from the mid 1990s. The gains seemed to be mainly caused by decreasing prevalence of low scorers. From the early 1970s, the secular gains in GA were almost exclusively driven by gains on the Raven-like test. However, even the means on this particular test stopped to increase after the mid to late 1990s. It is concluded that the Flynn effect may have come to an end in Norway. Height gains were strongly correlated with intelligence gains until the cessation of height gains in the conscript cohorts towards the end of the 1980s. Contrary to the intelligence gains, the height gains (conscript cohorts 1969–2002) were most pronounced in the upper half of the distribution. Evidence indicating decreasing intercorrelations between tests is reported.

This study investigates whether the Disruptive Behaviour Disorders (DBDs) rating scale measures the same constructs in South African as in Western cultures, and explores the differences in scale scores as a function of language, gender and age. Teacher ratings between 1997 and 1999 of the 18 DSM-IV symptoms of Attention-Deficit/Hyperactivity Disorder (ADHD) in 6 094 primary school children of six language groups in the Limpopo Province of South Africa were collected and analysed. For all language groups, the results were consistent with a two-factor model of ADHD with correlated factors. There were gender and age effects on both scales. The prevalence rates for ADHD sub-types were in line with rates in the United States of America (US) and Europe. Similarities across language groups, as well as to results reported in the US and Europe, were striking. Despite the limitations discussed, teacher ratings of ADHD symptoms on the DBD scale can be used as a screening instrument in South Africa. Separate norms for different language groups are not indicated.

The present study reports results from a study of the self-reported fears of identical twins and their spouses and offspring. Factor analysis with oblique rotation of questionnaire responses yielded four correlated fear dimensions: situational fears, illness-injury fears, social fears, and fear of small animals. Models allowing for genetic and cultural transmission, together with specially correlated environments for twins, were fitted, both for separate fears and across fears. Simple models with only genetic and uncorrelated environments were sufficient to account for each the fear dimensions considered separately. The cross-dimensional analyses revealed a genetic and an environmental factor common to the four fear dimensions, together with fear-specific genetic and environmental factors. The impact of the common genetic and common environmental factor varied across dimensions. No evidence of cultural transmission or specially correlated twin environments of the cross-dimensional environments was detected. It is concluded that both common and fear-specific genes and (individual-specific) common and fear-specific environments are necessary to account for the data. The results are discussed in terms of the prepared learning hypothesis and the expectancy bias hypothesis.

A school-based sex education program was developed in order to prevent sexually transmitted diseases and unwanted pregnancies. A Solomon four-group design, with random assignment to the different conditions, was used to evaluate an intervention based on cognitive social learning theory and social influence theory. The main goal of the intervention was to increase use of condoms. A stratified sample of 124 classes (2,411 students) was drawn at random from all the upper secondary schools (high schools/colleges) in one county in Norway. The results indicate a consistent interaction between pretest and intervention, which seems to have an effect on condom use. Pretest or intervention alone did not contribute to this effect. The interaction effect appeared among the students with few sexual partners. Several possible explanations to the observed interaction effect and the implication for future interventions are discussed.

The present study addresses the issue of differential heritability with increasing severity of parent-reported internalizing and externalizing behavior problems assessed by the Child Behavior Checklist. The sample includes 526 identical and 389 fraternal same-sexed twin pairs from five national birth cohorts, aged 5-6, 8-9, and 12-15 years. Heritability (h2), common environment (c2), and changes in these parameters as a function of proband score were analyzed by multiple regression models (Cherny et al., 1992). Internalizing and externalizing behavior showed significant heritability. A small increment in h2 and a reduction of c2 with increasing severity of externalizing behavior were independent of sex and age. For internalizing behavior h2 increased and c2 declined with increasing severity for the 5-6 and 8-9 year olds. Logarithmic transformation of scores lowered h2 and increased c2, particularly for externalizing behavior. The changes in heritability with severity were nonsignificant for the transformed variables.