Twin and family studies have reported, although inconsistently, sex effects on genetic factors underlying both neuroticism and extraversion.3, 18, 46, 47, 48, 49, 50 To investigate possible sex effects on the genetic variance of neuroticism and extraversion in the current design, significance of a genotype-by-sex interaction term was tested. We also estimated genetic variance explained by all the SNPs in sex-specific analyses. We investigated possible sex effects in both the total sample and in the Australian cohort only. Twin and family studies have generally suggested stability of genetic factors underlying both neuroticism and extraversion over age,3, 18, 46, 47, 48, 49, 50 others, however, suggested instability over age.50 Age effects were not investigated as age is confounded with the different study cohorts in the present study.
