Inherent in meta‐analyses is variation in study design and ascertainment methods used across studies. Although we have homogenized the analyses as much as possible, study cohorts have used different age groups, EEG apparatus and settings during recording, different genotyping platforms and biological sampling (saliva, blood), QC protocols, as well as different imputation algorithms. Spurious relations will largely be cancelled out by the meta‐analysis, and the consistent use of PCs, sex, age (group) and disease status covariates will have reduced these effects. However, remaining effects cannot be fully excluded, and may have decreased the power to detect associations. We acknowledge this limitation of our study.
