Strengths of the analysis reported herein include: (1) use of the same variable definitions (ie, the number of S alleles and an ordinal measure of life events) and analytic approach that was used in the original report in order to provide a valid test of replication; (2) inclusion of primary data from numerous studies to supplement the analyses of published data to maximize our ability to use a common framework across studies; and (3) our presentation of extensive analyses of expectations of gene-environment interaction in the absence of main effects, potential gene-environment correlation, and evaluation of whether stratification by an environmental risk factor will enhance power to detect a genotype-depression association.
