A final possible explanation for our results is that there may be interactive relationships among the variables, but limitations of our study prohibited their detection. Although our sample is the largest to examine associations between these 5-HT genes and bulimic phenotypes to date, it is still relatively small by molecular genetics standards (Hattersley & McCarthy, 2005). Power calculations indicate that we had adequate power (> 80%) to detect interactions of moderate effect (f2 = .15); however, our sample may not have been large enough to detect interactions of small effect (f2 = .05-.1). Similar to the main effects of single genes on complex psychiatric disorders (Cardon & Bell, 2001), interactions between genes and quantitative traits/environmental risk factors may represent effects of small magnitude. Therefore, an inability to detect significant interactions may have been due, in part, to a lack of power.
