Phenotype harmonization in GWAS consortia and collaborations involves a multi-stage process of 1) identifying commonalities and differences in phenotype data to assess the feasibility and potential benefit of combining data; 2) developing common data definitions for phenotypes of interest; and 3) creating and applying study-specific algorithms to convert data into a common format. The goal is to maximize the comparability and compatibility of data across datasets and to minimize inconsistencies and misclassification [Seminara et al., 2007]. The process must balance the need to augment the sample size which increases power for gene discovery with the likelihood of increased data heterogeneity which will decrease power to detect real effects.
