Genetic and environmental contributions to the relationship between education and anxiety disorders - a twin study.

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.

Changes in heritability across increasing levels of behavior problems in young twins.

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.

Genetic influence on parent-reported attention-related problems in a Norwegian general population twin sample.

OBJECTIVE: To assess the genetic and environmental influences on attention problems in a general population twin sample and to investigate whether there are changes in the relative genetic influence on attention problems with increasing severity. METHOD: Parental ratings of the Child Behavior Checklist were collected from five Norwegian national cohorts of same-sex twins. The sample comprises 526 identical and 389 fraternal pairs. RESULTS: Considerable genetic influence on attention problems was found for both sexes and across age groups (aged 5 to 9 years and 12 to 15 years). A two-parameter model with additive genetic influence and nonshared environment showed a good fit, with heritability ranging from .73 in boys aged 5 to 9 years, to .76 in girls aged 5 to 9 years. There was no change in the relative genetic influence across severity after accounting for the influence of cerebral palsy, epilepsy, and low birth weight. CONCLUSION: The results indicate a substantial genetic influence on attention problems across sex, age, and severity.

The effect of sex education on adolescents' use of condoms: applying the Solomon four-group design.

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.

PIP: This study involved the testing of a school-based sex education program in Norway which sought to prevent sexually transmitted diseases (STDs) and unwanted pregnancies by achieving an increased use of condoms. The intervention was based on cognitive social learning theory and social influence theory and was evaluated using a Solomon four-group design. The intervention involved the training of peer educators who spent two classroom days 1) identifying facts, 2) identifying situations and behavior that increased the risk of acquiring a STD or becoming pregnant, and 3) identifying the reasons why young people fail to use contraceptives and generating solutions that could be realized immediately. The peer educators developed the content of the education conveyed to younger peers (who were not studied). The random stratified sample contained 124 classes (2411 students). Of the 30 classes randomly assigned to receive the intervention, 15 classes answered the pretest questionnaire. Of the 94 control classes, 47 received the pretest. All classes were given two post-test questionnaires, one at six months and one at a year after the intervention. Individuals were used as the units of logistic regression analyses with the use of condoms as the dependent variable. The most important finding was the consistent interaction between the intervention and the pretest that seemed to have an effect on condom use. The intervention itself had no direct effect on behavior. The implications of these findings are that repetition is important in order to reach students at their most receptive period. This study also underscored the importance of using the Solomon four-group design which provides a control for the possible effect of interactions such as that observed between the pretest and the intervention.

Preferential looking: a sudden shift in visual fixation pattern at 32 months of age.

Observations of eye movements of young children in a modified preferential looking task suggest a change in the visual looking pattern taking place during a very brief time between 32 and 33 months of age. In the younger children, a grating stimulus elicited eye movements towards the target followed by a few seconds of focused attention; in the older children a visual avoidance behavior was observed where subjects looked consistently in the opposite direction of the target. An analysis of video recordings suggests that this avoidance pattern was a composite of a very brief initial target-directed eye movement which was quickly arrested, and followed by eye movements in the opposite direction, initiating a search of the visual scene.

No differential heritability of intelligence test scores across ability levels in Norway.

The possibility of differential heritability of intelligence test scores across levels of ability has been raised in several recent reports. In the present paper intelligence test data from 862 monozygotic and 1325 dizygotic male twin pairs tested at about 19 years of age were analyzed in search for changes in heritability and shared environmentality as a function of ability level. The analyses were performed by means of multiple regression models (e.g., Cherny et al., 1992). No evidence of differential heritability across different ability levels was detected.

Genetic and environmental effects on type A scores in monozygotic twin families.

Monozygotic (MZ) twin pairs with spouses and children, altogether 787 subjects, completed the Jenkins Activity Survey (JAS). The observed correlations for the various sets of relationships fitted well with biometric models including only parameters for additive genetic effects and, for Type A and Job Involvement, assortative mating. There was no evidence of effects of the family environment (cultural transmission) or genetic dominance (nonadditivity). For all but the Hard Driving and Competitive scale, there was evidence of effects of sex-specific genes. The heritability estimates were, for males and females, respectively, .33 and .39 for Type A, .36 and .48 for Job Involvement, .20 and .52 for Speed and Impatience, and .13 (both sexes) for Hard Driving and Competitive. The estimates given here are deflated by measurement errors and should probably be corrected by multiplying by values in the neighborhood of 1.3. Even after correction, the results suggest that individual differences for Type A and related traits depend more on nonfamilial environment than on genes.

Secular trends and sociodemographic regularities of coital debut age in Norway.

Gender and birth cohort differences and the influence of social background variables on the coital debut age were investigated in the general population of Norway. The data derive from a 1987 questionnaire on sexual behavior mailed to a random sample of 10,000 Norwegians of both sexes, ages 18 through 60; 63% responded to the questionnaire. 94.5% reported that they had experienced intercourse. The median coital debut age was 18.2 years. There were both cohort and gender differences. Younger cohorts have lower coital debut ages, and women younger than 35 years experienced their first intercourse at an earlier age than men in the same age group. When each independent variable was analyzed separately, there were substantial differences between educational levels and social classes with respect to age of coital debut. Multivariate analysis of six separate cohorts revealed independent effects of gender in the two youngest cohorts, whereas educational level had significant independent effects in all but the oldest cohort. Social class did not reveal any independent effect on coital debut age. Population density of the place of residence of the respondents was not substantially related to age of coital debut. Seen together, the independent variables explain about 13% of the variance in coital debut age (by multiple regression).

Use of birth control pills and condoms among 17-19-year-old adolescents in Norway: contraceptive versus protective behaviour?

This article addresses the relationship between sexual risk behaviour and contraceptive behaviour, and considers whether adolescents who use condoms are practising birth control or STD protective behaviour. The material comprised a representative sample of 3000 Norwegians aged 17-19 years. Data were collected by anonymous self-administered questionnaires. The response-rate was 63%. At the first sexual intercourse 51% of the adolescents used condoms and 7% birth control pills. At the most recent intercourse 31% used condoms and 38% the pill. Use of the pill was widespread among adolescents with high coital frequency and few coital partners. Use of condoms was not particularly widespread among adolescents who reported a relatively large number of coital partners. Irrespective of the number of years they had been coitally active there was no significant difference between those who intended to use condoms at the next sexual intercourse and those who did not as regards their beliefs about condoms as protection against STDs, HIV and unintended pregnancies. The results from this study indicate that the majority of adolescents who use contraception do this for protection against unintended pregnancy and not for protection against STDs. The preference for the pill may make teenagers less prepared to practise STD protective behaviour in specific situations.

PIP: A study was conducted to examine the relationship between coital frequency and risk behavior in relation to the number of coital partners and contraceptive/protective behavior and to study changes in contraceptive/protective techniques from 1st to most recent sexual intercourse. Data were gathered from 3000 Norwegians aged 17-19 years in anonymous self-administered questionnaires. A 63% response rate was achieved. 51% reported having used condoms at 1st intercourse, while 7% used contraceptive pills. 31%, however, used condoms most recently, while 38% employed the pill. Contraceptive pills were used most commonly among respondents with high coital frequency and few partners. Condom use was not particularly widespread among those with relatively large numbers of coital partners. Concerning beliefs about the ability of condoms to protect against sexually transmitted diseases (STD), HIV, and pregnancy, no significant differences were observed between those planning to use condoms and those not planning to use them at next coitus. In sum, results indicate that the majority of youths use condoms to protect against pregnancy, not STDs. The tendency toward serial monogamous relationships increases dependence upon the pill at the expense of the condom and makes sexually active teens less prepared to protect themselves against STDs in certain situations. Teens need to be taught about the protective value of condoms, with greater condom availability ensured where youths congregate.

The potential for spread of HIV in the heterosexual population in Norway: a model study.

A simulation model is used to investigate the potential for indigenous spread of human immunodeficiency virus (HIV) in the heterosexual population in Norway. The heterosexual population is grouped according to age, sex and whether paired or single. Estimates of various parameters of sexual behaviour are taken from a population-based questionnaire study. The questionnaire was sent to a random sample of 10,000 individuals, with a response rate of 63 per cent. The main simulation result is that with no inflow of infection from other risk groups, the heterosexual epidemic will decline if the average transmission probability per intercourse is 1 per cent or less. This result is insensitive to changes in the initial conditions. It is sensitive to changes in sexual behaviour, and to the shape of the transmission probability distribution. A review of empirical partner study data indicates an average transmission probability about 0.1 per cent per intercourse when no transmission modulating cofactors are present. It is concluded that with present sexual behaviour, the indigenous spread of HIV is not likely to sustain an epidemic in the Norwegian heterosexual population.

Pedigree analysis of Eysenck Personality Questionnaire (EPQ) scores in monozygotic (MZ) twin families.

MZ twins with spouses and children, altogether 811 subjects, completed the Eysenck Personality Questionnaire (EPQ). For extraversion (E), neuroticism (N), and lying (L), models including only additive genetic effects fitted well to the observed sex-specific correlations for the various sets of relationships. There was no evidence of sex differences for any parameter estimate for E, N, and L. The fit for E improved significantly after including dominance, and the fit for L improved significantly after including assortative mating. A model specifying genetic additive and dominance effects and assortative mating fitted well to the Psychoticism (P) data, but the fit improved significantly when a parameter for cultural transmission from fathers to daughters were included. Except for this, there was no evidence of cultural transmission for any scores. The heritabilities for the best-fitting models were .53 (E), .36 (N), .43 (L), and .39 (P). The latter includes almost only nonadditive, and no additive, variance, suggesting an overestimation of this effect due to random fluctuation or environmental sibling effect misinterpreted as dominance.

[Attitude towards use of condoms among Norwegian adolescents]. / Holdninger til bruk av kondomer blant norsk ungdom.

The article discusses the relationship between attitudes towards condoms and the use of condoms among sexually active Norwegian adolescents. The data stem from a random survey of 3,000 Norwegian adolescents aged 17-19. The responsrate was 61.8%. In general, most adolescents were positive towards condoms, and condom users were more positive than non-users. A logistic regression analysis showed that the only statistically significant predictors of condom use were the attitudes 'condoms aren't necessary to me' and 'condoms are uncomfortable'. The results indicate that attitudes towards condoms bear some relation to condom use. But, the use of condoms is also governed by factors other than attitudes.

[Use of condoms in relation to risk behavior among the heterosexual population in Norway]. / Kondombruk i forhold til risikoatferd i den heteroseksuelle norske befolkning.

In a questionnaire survey on sexual behaviour, a random sample of 10,000 Norwegians aged 18 through 60 were asked about use of condoms during their last intercourse. The response rate was 62.7%. Except as regards level of education, the response group was fairly representative of the population with respect to socio-demographic variables. About 12% reported use of condom. Among subjects who reported extra-marital partners, about 7% used condoms (both with their permanent and their extra-marital partner), whereas about 12% of subjects who did not have extramarital sex used condoms. 15% of the single persons reported use of condom. Apparently, the use of condoms is not related to sexual behaviour correlated with risk of HIV-infection, such as the number of partners and knowledge about the partner. Neither is perceived risk, as measured by HIV-testing behaviour, related to the use of condoms.

Genetic and environmental contributions to the covariance between occupational status, educational attainment, and IQ: a study of twins.

Scores of occupational status, educational attainment, and IQ were obtained for 507 monozygotic and 575 dizygotic male twin pairs born 1931-1935 and 1944-1960. A multivariate genetic analysis with statistics from different cohorts showed heterogeneity between cohorts, and analyses were performed in four separate cohorts. The only set of results which departed clearly from the rest was found for the group born 1931-1935, where the ratio of environmental to genetic effects exceeded those of the other groups. Typical heritability values in the three youngest groups (weighted means) were .43, .51, and .66 for occupation, education, and IQ, respectively. The values in the oldest group were .16, .10, and .37, but this sample is small and the estimates are unstable. Genetic variance influencing educational attainment also contributed approximately one-fourth of the genetic variance for occupational status and nearly half the genetic variance for IQ. The values for the between-families variances (reflecting family environment and assortative mating) varied from 2 to 35% in the three youngest groups but were higher for education (62%) and IQ (45%) in the oldest groups. All the between-families variance was common to all three variables. For educational attainment and IQ, the bulk of this between-families variance is probably genetic variance due to assortative mating. The common-factor environmental within-family variances were generally small, and the specific estimates seemed to contain mainly measurement error.

Cotwin closeness in monozygotic and dizygotic twins: a biasing factor in IQ heritability analysis?

For 98 pairs of MZ twins, four measures indicating degree of cotwin closeness were correlated with absolute differences between IQ scores within pairs. In two different twin samples (40 MZ vs 40 DZ pairs and 169 MZ vs 174 DZ pairs, respectively), means and standard deviations in the closeness variables were obtained for MZ and DZ pairs. Whereas MZ cotwins were clearly closer than DZ cotwins, the relation between cotwin closeness and similarity in IQ seemed rather weak and ambiguous. "Years lived together in childhood home" were positively related to similarity in IQ (P less than 0.01), whereas subjective feeling of closeness in contact tended to be negatively related to similarity in IQ.