in each subsample. This is a highly conservative control for MAOA and essentially eliminates it as a potential confounder of their G×E finding, but the investigators did not control for their other covariate (gender) in the same way and did not control for any other potential confounders. Similarly, Amstadter et al. (28) and Ǻslund et al. (29) restricted follow-up analyses to ethnically homogeneous subsamples and found similar results to their original ones, eliminating stratification as a possible alternative explanation to their findings. However, the datasets were not similarly stratified on other covariates. Finally, the study by Waldman (30) was the only one of those investigated that included several covariate-by-gene (in this case) interaction terms in the primary model to eliminate several alternative explanations for the G×E finding, but the study failed to control for other covariates such as ethnicity in a similar way.
