scores (Mean (M) = 0, standard deviation (SD) = 1) extracted from CFA models using all individuals of European descent. Genetic analyses of DV utilized rank normalized scores (using the BLOM approximation method (34); M = 0, SD = 1). These analyses yielded a factor score based on the dichotomous DSM-IV diagnoses of “drug dependence” (DD) and a factor score of “problem usage” (PU) that was based on items measuring the presence or absence of at least one of the seven total substance dependence symptoms for each of the five diagnostic categories. Unlike recent GWAS studies using factor scores based on dependence diagnoses, DV has previously been shown to localize regions of interest using linkage analysis (29).
