Abstract

ABSTRACT Previous behavior‐genetic research on personality has been almost exclusively based on self‐report questionnaire measures. The purpose of this research was to measure personality constructs via self‐ and peer reports on the items of the NEO Five‐Factor Inventory (Costa & McCrae, 1989). The sample included 660 monozygotic and 200 same sex and 104 opposite sex dizygotic twin pairs. We collected self‐ and two independent peer reports for each of the twins. Our analysis of self‐report data replicates earlier findings of a substantial genetic influence on the Big Five ( h 2 = .42 to .56). We also found this influence for peer reports. Our results validate findings based solely on self‐reports. However, estimates of genetic contributions to phenotypic variance were substantially higher when based on peer reports ( h 2 = .51 to .81) or self‐ and peer reports ( h 2 = .66 to .79) because these data allowed us to separate error variance from variance due to nonshared environmental in‐fluences. Correlations between self‐ and peer reports reflected the same genetic influences to a much higher extent than identical environmental effects.