Meta-analysis has thus become essential in human complex trait genetics. There are now many examples where meta-analyses combining dozens of primary data sets have illuminated the genetic architecture of complex traits such as height,29 body mass,30 Crohn’s disease31 and Type 2 diabetes mellitus.32 Following this proven model, we created the Psychiatric GWAS Consortium (PGC)33,34 to conduct field-wide combined analyses for MDD as well as ADHD,35 bipolar disorder (BIP),36 schizophrenia37 and autism. Our goal was to evaluate the evidence for common genetic variation in the etiology of MDD using the largest and most comprehensively genotyped sample hitherto collected.
