A family history density (FHD) score 65 was calculated for each participant in both samples. FHD scores were based on degree of biological relatedness, in which parents and full‐siblings with a lifetime history of DSM‐IV alcohol dependence contributed 0.5 for each person, each dependent grandparent or sibling of parents contributed 0.25, and non‐affected biological relatives contributed zero. We calculated FHD as the sum of weights divided by the number of counted relatives. A detailed description of Materials and Methods is provided in Supporting Information.
