but no effect of GxE. Caution is advised when using this approach. It is well known that mean-centering of (quasi)continuous variables is requisite for removing any collinearity between an interaction (i.e., product) term and its component predictors, and avoids spurious results (Aiken and West 1991). Given proper treatment of genetic and environmental indicators, GxE interaction can be formally tested in many statistical models, including linear mixed models.
