The purpose of the present study is to estimate the proportion of the phenotypic variance of neuroticism and extraversion explained by considering all SNPs on currently-used genome-wide arrays simultaneously.43, 45 The basic idea of this method is to accumulate the effects of all the associated SNPs that might be too small to reach the stringent significance level in single SNP analyses. To this end, we analysed the neuroticism and extraversion personality trait scores, measured in ∼12 000 unrelated individuals from combined samples from Australia, Sweden, the United Kingdom and the United States of America.
