The present study offered several strengths for evaluating G×E. First, we studied two large, representative cohorts with highly complete follow-ups, thereby obviating problems associated with selective attrition which affect the frequency of exposure to severe stress and thereby the evaluation of G×E (Shanahan and Bauldry, 2011). Second, we used the same diagnostic instruments in both cohorts and on multiple occasions, thereby avoiding problems associated with comparing findings across samples that differ in phenotypic ascertainment. Third, we conducted parallel analyses across both cohorts allowing us to evaluate what replicates and what does not. We also note several limitations to our study. First, our study was limited to individuals of European ancestry. Although studies of Asians (Goldman et al., 2010) and African-Americans (Xie et al., 2009) have documented that carriers of 5-HTTLPR short alleles are more likely to develop a variety of stress-related psychiatric conditions, the present findings about the importance of longitudinal phenotypes will need to be evaluated in other ethnic groups. Second, the assessment of depression relied on four noncontiguous one-year assessment windows. Thus some recurrent cases might have been
