The two examples encourage the view that some endophenotypes may be more genetically tractable than the ones we have discussed. Our concern is that as additional data accumulate these findings may turn out to be false positives, or at least the effect sizes will be much smaller than initially reported, as has often been found with genetic association studies (Trikalinos et al. 2004). Indeed, removing samples from the first published study in our analysis of WCST data rendered the association with COMT genotype non-significant and reduced the pooled effect size estimate by 20%.
