Frequency × quantity was a composite of 2 items; the frequency of reported alcohol use in the past 28 days multiplied by the quantity of drinks (drinks defined as 1 beer, 1 glass of wine, or 1 mixed drink containing hard liquor) consumed per drinking day during the past 28 days. Because this measure was highly skewed, with over representation of those who drank on less than 1 occasion in the past 28 days, we log-transformed this variable.
