One limitation was that 1000 Genomes imputed results were unavailable in ICBP; however, the much larger UKB replication did not have this limitation. For ICBP, we therefore relied on summary test statistic imputation from HapMap. The use of these approximated results, and the fact that all test statistics from ICBP were based on SNP results imperfectly imputed to HapMap, likely led to diminished effect sizes in ICBP. Overall, we needed a very large number of individuals for replication, both to replicate our novel GERA results, which improved greatly when adding UKB to ICBP, and to replicate previously-described results, which improved when adding UKB to GERA.
