Genetic and Environmental Influences on Two Measures of Speed of Information Processing and their Relation to Psychometric Intelligence: Evidence from the German Observational Study of Adult Twins

Speed of information processing, as measured by reaction times (RTs) in elementary cognitive tasks (ECTs), has been found to be an important correlate of human psychometric intelligence. While the heritability of psychometric intelligence is well understood, we know only a little about genetic and environmental influences on ECT performance, particularly about genetic and environmental contributions to ECT–intelligence relation. These questions were studied by employing two widely used ECTs (Sternberg's memory scanning and Posner's letter-matching task) as well as two psychometric intelligence tests (Advanced Progressive Matrices and Leistungs–Prüf System) in a large sample of 169 monozygotic (MZ) and 131 dizygotic (DZ) twin pairs. As expected, RTs correlated negatively with psychometric intelligence. Moreover, heritability estimates were substantial for both psychometric intelligence and RTs in ECTs. Finally, multivariate genetic analyses suggested that most of the phenotypic correlation between mental speed and intelligence is due to genetic factors.     

A behavioral genetic study of the overlap between personality and parenting

The current study had three aims. The first was to examine the covariation between personality of parents and parenting behaviors. The second aim was to examine the genetic and environmental influences on parenting behaviors. The third aim was to examine the extent to which the association between personality and parenting was mediated by genetic and environmental factors. Personality (Five Factor Model, NEO-FFI) and parenting data were collected as part of a larger German study of 300 adult twin pairs (GOSAT). The current paper analyzes data on a subset of the 300 twin pairs from the GOSAT sample who were concordant for having children (n=98 pairs or 196 individuals). Results indicated modest overlap between personality and parenting. In addition, univariate behavioral genetic analyses indicated moderate genetic influence on select parenting dimensions. Results also indicated that the moderate phenotypic covariation between personality and parenting was attributed largely to nongenetic factors. Implications of the findings for research on parenting and personality are considered.     

Genetic and environmental influences on personality profile stability: unraveling the normativeness problem

The present study is the first to disentangle the genetic and environmental influences on personality profile stability. Spanning a period of 10 years, we analyzed the etiology of 3 aspects of profile stability (overall profile stability, distinctive profile stability, and profile normativeness) using self- and peer reports from 539 identical and 280 fraternal twins reared together. This 3-wave multirater twin design allowed us to estimate the genetic and environmental effects on latent true scores of the 3 aspects of profile stability while controlling for method effects and random error. Consistent biometric results were only found for profile normativeness, whereas overall and distinctive profile stability scores turned out to be biased. Over time, we found personality profile normativeness to be relatively stable. This stability was due to both stable genetic and nonshared environmental effects, whereas innovative variance was completely explained by nonshared environmental effects. Our findings emphasize the importance of distinguishing between the different aspects of profile stability, since overall and distinctive stability scores are likely biased due to the normativeness problem. Yet indicating a person's similarity to the average person, the normativeness of a personality profile itself has a psychological meaning beyond socially desirable responding.     

Motivation as a Mediator of Social Disparities in Academic Achievement

The present study aimed at contributing to the understanding of social disparities in relation to students' academic achievement in the science, technology, engineering and mathematics domains. A sample of n = 321 German 11th graders completed measures of their family socio‐economic status (SES), general intelligence, domain‐specific ability self‐concepts and subjective scholastic values in math, physics and chemistry. Students' grades in these subjects received four months after testing served as criteria. Significant mediation effects were found for all motivational variables between fathers' SES and students' achievement, whereas for mothers' SES, only children's academic self‐concept in chemistry was a significant mediator. These results also held when students' general intelligence was controlled. Additionally, we controlled for students' grades before testing to investigate which variables mediated the influence of SES on change in school performance. Motivational variables significantly mediated the influence of fathers' SES on change in school performance in math but not in chemistry and physics. Intelligence significantly mediated the influence of fathers' SES on change in school performance in physics and chemistry but not in mathematics. The impact of mothers' SES on change in grades in chemistry was mediated by intelligence. Among others, the reasons potentially accounting for the differential influences of fathers' and mothers' SES are discussed. Copyright © 2011 John Wiley & Sons, Ltd.