with nicotine and alcohol dependence, respectively. However, even the considerable body of “failed” studies were quite informative. The expectation that individual genetic variants would be associated with psychiatric disorders at a magnitude that would be small but detectable with hundreds, or a few thousand individuals (Hirschhorn & Daly, 2005) was found to be untenable, and we learned that the risk contributed by any single variant was likely to be tiny rather than just small, with odds ratios on the order of less than 1.1 (O’Donovan, 2015), necessitating much larger sample sizes to be able to detect them. In recognition that the necessary sample sizes would be practically impossible for nearly any single research study to achieve, scientific groups began to collaborate in order to pool resources and participant data into consortia for meta- and mega-analysis (Psychiatric GWAS Consortium Steering Committee, 2009).
