We included age, sex, birth cohort, and the first ten genetic ancestry principal components (PC1–10) in all analyses. Birth cohort was indexed using four dummy coded variables following the generation status scheme (Bourdon et al., 2020): silent [prior to 1945]; baby boomer [1946 to 1964]; generation X [1965 to 1980]; and millennial [1981 to 1996], with baby boomer set as reference.
