Awareness of the need for large sample sizes for GWAS has resulted in the formation of large scale collaborations for sharing data, such as the Psychiatric Genomics Consortium [82]. However, one risk of this approach is to potentially increase phenotypic heterogeneity. Qualified investigators can access freely available GWAS datasets via the database of Genotypes and Phenotypes (dbGaP) [83] and several studies have used this resource for replication samples.
