Unless one's sample is unusually large or unusually special, conducting a genetic association study of common variants and complex disorders/traits is expected to produce entirely null results or, on the rarest of occasions, it will produce significant results that then require extensive replication. There are multiple ways to conduct replication studies, and here we may differ with others in our recommendations. Our recommended approach is not to replicate, in the traditional sense where only the significant variant is replicated in an independent sample at p<.05, but to conduct GWAS meta-analyses. In this approach summary statistics (e.g., effects and p-values) are generated in each independent sample for every imputed variant, and then those summary statistics are combined into one meta-analytic result per variant. If each study imputes 45 million variants, then there will be 45 million results from a GWAS meta-analysis of those studies.
