Alcohol consumption at each assessment was measured by a question adapted from the Semi-Structured Assessment for the Genetics of Alcoholism (SSAGA-IV) (Bucholz et al., 1994) that assessed participants’ frequency of drinking: “On how many days did you drink any beverages containing alcohol during the last 12 months?” The responses included 13 categories ranging from 0 (Never) to 12 (Every day). Because the categories were not in equal intervals, we converted the responses into number of drinking days per year by taking the midpoint of each category. For example, the categories “Every day” and “2 days per week (100–149 days)” were converted into 365 and 124.5 days per year, respectively. Those who reported not drinking during the past year skipped the question, and their answers were recoded into zero. Alcohol dependence (AD) was measured at each assessment as part of the SSAGA-IV interview. AD status was determined based on the diagnostic criteria for AD according to the Diagnostic and Statistical Manual of Mental Disorders 4th edition (DSM-IV, American Psychiatric Association, 2000). AD was coded into a binary variable (0= absence of
