We do acknowledge a number of limitations to the current study. The size of our sample is modest, which limits statistical power. Furthermore, our analyses are limited to a Caucasian population due to the small number of minority individuals participating in the Child Development Project; while this reduces the likelihood of population stratification, we cannot say with absolute certainty that no stratification exists. The effects of genotype and physical discipline on externalizing behavior and its components should be explored in larger samples. Finally, due to the highly correlated nature of these analyses, correction for multiple tests is not straightforward and has not been applied to our results.
