mixed model (Barton, 2011; Nakagawa & Schielzeth, 2012). We use the marginal R2 to select the most predictive pT. The proportion of variance attributable to the PRS (Δmarginal R2) was estimated as the difference between the marginal R2 (i.e., Δmarginal) of the model that included covariates and the PRS and the model with covariates alone (i.e. marginal R2(full model) - marginal R2(model without PRS)). Further, Cox proportional hazards survival analyses for onset of DSM4AD were conducted using the survival and survminer packages in R (Kassambara, Kosinski, & Biecek, 2017; Therneau & Lumley, 2015) with the same covariates as above. Violations of the proportional hazards assumption for the PRS were tested using scaled Schoenfeld residuals. For graphical depiction of cumulative survival curves, quartiles of PRS were computed and hazard ratios were estimated across those categories, with adjustment for covariates. Family membership and recruitment site were included in the survival models using the “cluster()” function, which produces a robust estimate of standard errors that accounts for potential clustering on those two variables (Therneau & Grambsch, 2013; Therneau & Lumley, 2015).
