Measurement of outcomes

There were two outcome measures used in the study. Alcohol consumption was measured at the age of 17 years using a computerised questionnaire, which was completed by the young person in a clinic setting. The questionnaire included the Alcohol Use Disorders Identification Test (AUDIT)⁽²⁶⁾ and AUDIT score was used as the first outcome measure. Clinically, a score of 8 or more in the AUDIT test is considered to indicate an increased risk of harm from alcohol^(26,27), and we therefore chose to use this dichotomy.

The second outcome was a measure of the frequency of alcohol consumption and was based on responses to a question that asked how often the young person had a drink containing alcohol. The options were never, monthly or less, 2 or 4 times a month, and 2 or 3 times a week or 4 or more times a week. We collapsed the five categories into ‘at least weekly’ (‘2 or 3 times a week’ and ‘4 or more times a week)’ compared with less than weekly: (‘never’, ‘monthly or less’ and ‘2 or 4 times a month’) in order to facilitate comparison with the IDEFICS study⁽¹⁰⁾.