The present results, in combination with previous findings, indicate that variants of moderate or large effect do not play a role in variation in personality in the population - if they did, GWA studies should have found the common variants, and linkage studies should have found rare variants. This narrows the search to common and rare variants of small effect. Current GWA methods with increasingly large sample size will enable identification of common variants of ever-smaller effect size. However, current methods do not allow investigation of accumulated rare variants of small effect, which may play a substantial role in personality and other traits. A key challenge is to develop genotyping technologies and statistical approaches for quantifying mutation load across the genome (e.g. how many mutations (very rare alleles) an individual’s genome contains). In this regard, the dual problem with current GWA methods is that 1) rare variants are not included on SNP chips, and 2) the rarer a variant is, the less reliably the genotype can be determined. Whole genome sequencing, which will become feasible in large samples in the
