Genetic and environmental influences on the EPQ-RS scales: a twin study using self- and peer reports

We examined genetic and environmental influences on the scales of the German Eysenck Personality Questionnaire-RS (EPQ-RS) in a sample of 496 monozygotic, 181 same-sex, and 68 opposite-sex dizygotic adult twin pairs. Along with other questionnaires each participant completed the EPQ-RS and was also described by two independent peers on a peer report form of the EPQ-RS. Based on this design it was possible to analyse not only the standard univariate twin model but more powerful multivariate models to estimate the genetic and environmental sources of variance on phenotypic individual differences. Partly because latent variables are error free, the joint analyses of self- and peer report data yielded genetic contributions to phenotypic variance that were substantially higher than typically found in univariate analyses based on self-report data alone (h2=0.67–0.86). These high genetic correlations between self- and peer reports provide evidence for the validity of personality ratings.