Although we cannot know how often this kind of joint effect might occur, we find this result, displayed in COGEND data, ACS data, and the larger CGASP data, a strong argument that tests for interactions not be limited to loci with substantial main effects, and that the consideration of joint effects should not be limited to ones giving rise to a statistically significant interaction term. It is an advantage of the RPM, focused on identifying sources of trait variance and not specifically interactions, that it identifies such pairs in an automated fashion, without the need to examine each model individually (an impractical approach when evaluating many thousands or millions of multi-locus models).
