Because the current sample was selected for alcohol dependence, it should be noted that prevalence rates for the cannabis dependence diagnoses and respective symptoms in the unselected control sample were estimated and included in the tested models to correct for ascertainment bias when calculating h2 and linkage. In addition, the high marker density of the HD5 microsatellite panel allows for the extraction of a large proportion of IBD information among relative pairs as participants' genotypes can be almost completely phased, thus reducing the reliance on population allele frequencies to estimate allele-sharing probabilities. As a result, and given the very low number of ethnic minority participants in the UCSF sample, we chose to include all participants in the analyses without correcting for ethnic background.
