phenotypic and environmental measures such that meta-analysis or harmonization is difficult to impossible, and the success of exploratory GEWIS becomes less promising. Unless an a priori GxE hypothesis is extremely strong or the environmental effect is severe and/or uncommon (Caspi, et al., 2010), it is preferable to filter SNPs from genome-wide arrays according to criteria that are likely to result in a subset of SNPs that have promise of environmental interaction (Sullivan, et al., 2009). GxE tests can then commence on the presumably much smaller subset of filtered SNPs.
