Manolio & Collins, 2009), like linkage studies, early GWAS were largely unsuccessful in the area of psychiatric and substance use disorders (K. S. Kendler, 2013). Few SNPs were detected that met genome-wide levels of significance. As increasingly large sample sizes have been procured, we now know that most early GWAS were simply underpowered (Visscher, Brown, McCarthy, & Yang, 2012). Amassing sample sizes through large consortia on the order of tens of thousands or more has revealed that the number of significant findings increases as the sample sizes increase.
