It is also important to note that not only are there several scenarios that would lead one to make incorrect conclusions about the nature of a gene-environment interaction effect, there are also scenarios that would lead one to conclude that a gene-environment interaction exists when it actually does not. Several of these are detailed in a sobering paper by my colleague Lindon Eaves, in which significant evidence for gene-environment interaction was detected quite frequently using standard regression methods, when the simulated data reflected strictly additive models (Eaves 2006). This was particularly problematic when using logistic regression where a dichotomous diagnosis was the outcome. The problem was further exaggerated when selected samples were analyzed.
