Chunk #11 — Three examples of misspecified models in the G×E literature — Kaufman et al., 2004: A gene-by-environment or an ethnicity-by-environment interaction?
Kaufman et al. (20) reported their 5HTTLPR-by-maltreatment interaction in a model that also tested a two-way 5HTTLPR-by-social support interaction (ns) and a three-way 5HTTLPR-by-maltreatment-by-social support interaction (p=.0001). This raises two issues. First, in models testing three-way interactions, investigators must include not only all relevant two-way covariate-by-gene and covariate-by-environment interactions, but must also include all relevant three-way interactions involving the covariate. With small sample sizes, this can eat up a relatively large number of available degrees of freedom, but it is necessary if investigators wish to eliminate these covariates as explanations for their interaction results.
