tens of thousands of samples from multiple independent studies in order to identify the effects of common variants with small effect sizes (29). However, caution needs to be taken to ensure that these large sample sets are not collected at the expense of detailed environmental and behavioral information, or do not limit the use of intermediate phenotypes, and that internal heterogeneity within studies does not offset the advantage of increased sample size. These meta-analytic studies are designed to detect the residual main genotype effects, and likely identify only those variants whose main effects are large enough to be detectable against the backdrop of the myriad different environments from which these samples are taken.
