If the analyses were based on only the SNPs that were in common between all the study cohorts, estimates of the heritability were slightly lower (See Figure 1 and Supplementary Information Table S2). This is expected because a less dense SNP set (162 056 versus 871 333) provides lower LD between the genotyped SNPs and the unknown causal variants. Analyses with and without the first 20 principal components included as covariates in the model revealed very similar results, implying that any population stratification that was observed within our European-ancestry sample had a negligible effect on the results. The analyses were repeated for subsets of the sample (Figure 1 and Supplementary Information Table S2). Separate study-cohort analyses showed a fairly inconsistent pattern reflecting larger s.e., but generally estimates were lower for neuroticism than for extraversion. Study-cohort separate analyses based on only the 162 056 SNPs that were in common between all study cohorts showed a similar pattern as the analyses based on all the SNPs, suggesting that different estimates between study cohorts are not a result of different SNP arrays that
