At waves 4 to 7, participants were requested to provide the number of close friends they had. At wave 4, a follow up question asked ‘how many of those close friends drink alcoholic beverages?’ In waves 5 to 7, a follow up question inquired how many of those friends ‘do you consider to be heavy drinkers?’ Friends' alcohol use was computed as the percentage of close friends who drank alcohol (wave 4) or were considered heavy drinkers (waves 5-7).
