Third, diseases can have differences in prevalence across populations. While a large portion of this variation undoubtedly results from non-genetic factors, disease prevalence affects both the practicality of obtaining the large sample sizes required by GWA studies for detecting variants with small effects and the relevance to a population of the findings. A limited population focus risks underemphasis of diseases for which prevalence is high in non-European populations, or reduced power compared to potentially larger samples that could be obtained in higher-prevalence populations.
