PER2 and sleep disorder: The sample size for different test efficacies in case-control studies was estimated using the PASS software package; sample size was calculated based on prior studies showing that PER2 polymorphisms are associated with sleep disorders (OR = 1.5, α = 0.05, β = 0.2), which resulted in a sample size of 368, and 374 subjects in each of the case and control groups in this study, which was in line with the requirements of the sample size.