The inflated false positive rate due to multiple testing, the issue of population stratification that can confound associations and technical errors that can be committed during the collection of DNA samples, and the analysis require the replication of the results from GWAS in at least one independent study to guarantee their validity [98]. Replication should not be confused with technical validation of the genotype data that requires genotyping a small set of SNPs with a different technology. This strategy is highly recommended in [98] but not very often adopted or reported. It has been suggested that a convincing replication should use a larger sample from an independent study population, with the same genetic background of the primary study population, the same definition of the phenotype, and should report the association of the same SNPs with the same genetic model and show the same genetic effect. Inclusion of proxy SNPs that are in high LD is still an open issue: some authors recommend this practice as further evidence of a real association [98] while others recommend against it because it is
