GWAS have increased statistical power by adding clinically or pathologically diagnosed cases and controls. This method is time–consuming and expensive due to the extensive efforts needed for recruitment, ascertainment, and genotyping. With the advent of large biobanks such as the UK Biobank (>500 000 participants), large population-based cohorts of genotyped individuals are now available. However, ascertainment of Alzheimer’s disease cases is limited in these biobanks because enrolled participants tend to be too young to have a high probability of developing Alzheimer’s disease; in the UK Biobank, only about 1000 individuals have a diagnosis of Alzheimer’s disease, based on International Classification of Diseases 10 codes. Genome–wide association studies by proxy (GWAX)17 are a novel solution to this problem, using parental history of a trait to identify proxy cases and controls. This approach requires approximately four times as many proxy cases and controls for equivalent power to traditional GWAS. However, GWAX can massively increase statistical power compared with GWAS due to a larger sample size by including younger samples from large biobanks.17 Unknown sample overlap in meta–analysis of cohort studies can lead
