There are a large number of consortia undertaking GWAS analyses (Table 3) and the phenotypes under investigation by various consortia often overlap. Negotiations with other consortia WGs can lead to collaborations where GWAS investigators can contribute to data analyses being led by other consortia. This benefits both groups—investigators are able to contribute to primary analyses of an important phenotype and the collaboration's primary analyses now include data on additional individuals. Studies that are still being genotyped can contribute to later analyses. Alternatively, investigators may decide to serve as a replication study or look at other related or intermediate phenotypes or associations and G*E analyses beyond the initial ones being conducted. There are, of course, implications of overlapping data across independent meta-analyses and in some instances, such overlap is unavoidable. In those instances, appropriate corrections, such as those described by Lin & Sullivan [Lin DY and Sullivan PF, 2009], might be considered.
