Methods for testing interactions reflecting differential susceptibility have been proposed (e.g., Belsky et al., 2007; Belsky & Pluess, 2009; Ellis et al., 2011) and applied to GXE data (e.g., Bakermans-Kranenburg, Van IJzendoorn, Pijlman, Mesman, & Juffer, 2008). Our goal is to develop a more direct test of competing predictions regarding the ordinal vs. disordinal nature of an interaction that is widely applicable across research domains, including GXE studies.
