THE GENETIC STRUCTURE OF PERSONALITY Ill. MULTIVARIATE GENETIC ITEM ANALYSIS OF THE EPQ SCALES

Summary-Multivariate genetic item analyses were performed, separately for the EPQ £, N, Land P scales, using data from 2903 like-sex pairs from the Australian Twin Register. For cach scale, a constrained multivariate genetic model was fitted, which postulates that genetic and environmental inftuenoes which are 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 SI, 41-31:1d 16 % (for males) and S3, SI 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 inftuenoes 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 environmental inftuenoes 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