In our primary GWAS of subjective well-being, we also used two family-based analyses to test for and quantify stratification biases. These analyses used within-family (WF) estimates, the coefficients from regressing the difference in phenotype across siblings on the difference in siblings’ genotype (and controls). These WF estimates are not biased by population stratification because siblings share their ancestry entirely, and therefore differences in siblings’ genotypes cannot be due to the siblings being from different population groups. We meta-analyzed association statistics from WF analyses conducted in four cohorts.
