Q:
I am writing with a question about the cQTL analysis in Wang et al 2018. Were the 292 individuals analyzed in this analysis all of European ancestry? If not, what were the sample sizes for European vs non-European ancestry, and how did you control for ancestry in your analysis?

I apologize for writing with such a detailed question, but I could not find the answer in the main text or supplement of the paper, or on the synapse website. (Context: I am interested in cross-population genetic analyses of psychiatric disease and wondering if PyschENCODE cQTL data is relevant.)

A:
In calculating the cQTLs, we used 173 Caucasians and 119 non-Caucasians. With respect to controlling for ancestry — we used the top three genotype principal components as covariates to control for ancestral group.