In the mailed questionnaires, drinking frequency was assessed by the item “Write in below the number which best describes how often the following people have had alcoholic drinks DURING THE PAST 12 MONTHS”. The telephone interview question regarding drinking frequency was “During the past 12 months, how often have you had alcoholic drinks?”. Response choices varied slightly between studies. They were recoded into the following 6 categories that are common to both the telephone interview and earlier mailed questionnaire studies (6 = at least once daily, 5 = 3–6 days per week, 4 = 1–2 days per week, 3 = 1–3 days per month, 2 = less often, 1 = never).
