In the discovery stage, we conducted a GWAS megaanalysis for MDD in 18 759 independent and unrelated subjects of recent European ancestry (9240 MDD cases and 9519 controls, Table 1). There were considerable similarities across samples: all subjects were of European ancestry, all cases were assessed with validated methods and met DSM-IV criteria for lifetime MDD, and most controls were ascertained from community samples and screened to remove individuals with lifetime MDD (Supplementary Methods and Supplementary Figures S6–S9).
