Risk scores were therefore linear combinations of the included SNPs, weighted by their training-sample-derived regression coefficients. The ability of this score to cross-predict testing sample variance in cocaine dependence scores was estimated as the correlation between the summed risk score and cocaine dependence symptoms (which had been residualized over covariates, i.e., sex, age, study source, and ancestry, as described for the training set). Specificity of the aggregate cocaine SNP score was investigated by correlating the cocaine-derived SNP score with substance dependence symptoms for alcohol, nicotine, and marijuana, each of which were residualized over the same covariates.
