GWAS have successfully identified genetic loci associated with a variety of conditions such as type 2 diabetes (2) and coronary disease (3–5). The large number of statistical tests required in GWAS poses a special challenge because few studies that have DNA and high-quality phenotype data are sufficiently large to provide adequate statistical power for detecting small to modest effect sizes (6). Meta-analyses combining previously published findings have improved the ability to detect new loci (2). Even before the era of GWAS (7), the requirement for large sample sizes and the importance of replication have served as powerful incentives for collaboration.
