original_query: What is the genotype-first approach used for in genetic epidemiological studies?
query: What is the genotype-first approach used for in genetic epidemiological studies?
answer: In genetic epidemiological studies, the genotype-first approach associates specific genotypes with clinical phenotypes of complex diseases or traits.  It characterizes individuals by a common genotype before clinical classification, preventing phenotypic bias and identifying genes significantly contributing to disease etiology.