The raw total on the 12-item neuroticism subtest of the Eysenck Personality Questionnaire-Revised62 (maximum score = 12) was used as the target phenotype for out-of-sample prediction. Both genetic and neuroticism target data was available on 19,876 European participants in the Generation Scotland cohort63. Neuroticism scores were residualized for age, sex, and 20 principal components of ancestry prior to examining out-of-sample prediction. PGSs were constructed using PRSice,61 with LD clumping set to r2 > 0.25 over 250kb sliding windows and using a p-value threshold of 1.0. PGSs for neuroticism were based on the WLS summary statistics produced using Genomic SEM. Regression analyses were run using the lmekin function within the coxme package in R with a random intercept to account for nesting of individuals within families.
