The genetic structure of personality III. Multivariate genetic item analysis of the EPQ scales

Multivariate genetic item analyses were performed, separately for the EPQ E, N, L and P scales, using data from 2903 like-sex pairs from the Australian Twin Register. For each scale, a constrained multivariate genetic model was fitted, which postulates that genetic and environmental influences which a common to the items of the scale are mediated through a single latent phenotype ('latent phenotype model'). Results for Extraversion, Neuroticism and Lie scales were in good agreement with conventional analyses of scale scores, yielding broad heritability estimates of 51, 47 and 16% (for males) and 53, 51 and 46% (for females). Evidence for genetic nonadditivity was obtained not only for Extraversion but also for Neuroticism items (particularly in males). No evidence was found for heritable influences on the Psychoticism latent phenotype, contrary to reports based on conventional analyses of scale scores. This discrepancy is apparently explained by the very different structure of genetic and envitonmental influences on responses to P items: although there are common genetic effects on the P-scale items, the multivariate structure of these effects is not at all consistent with predictions for Psychoticism.