Common SNPs explained between 4.2% and 9.9% of the total variation in the four personality traits, at an average of 7.2% (Table 3). Due to the large sample size, the standard errors of these estimates were small (~3.7%), and estimates for Harm Avoidance, Novelty Seeking and Persistence were significantly different from zero (p<.05). Correcting for incomplete LD between the SNPs and causal variants, or almost doubling the number of SNPs used, had a negligible effect on the estimates (see Supplementary Table 6), indicating that our estimates captured the vast majority of all common additive genetic variant effects. Re-running the tests without the 20 principal components as covariates increased the estimates only a little (see Supplementary Table 6), and re-running analyses with a more stringent cut-off for relatedness (0.025) somewhat lowered the estimates for Harm Avoidance, Novelty Seeking and Persistence (see Supplementary Table 6), suggesting that our main estimates (Table 3) could be slightly inflated due to causal variants not correlated with SNPs but captured by pedigree. As such, the estimates in Table 3 are best considered upper limits, reinforcing that common additive genetic variant effects play only a minor role in personality variation.
