Hard, but not as much as you think. Consequently, given these distributions, a single smoking composite across the assessments was created for each youth: Smokers were defined as youths who reported smoking at all three assessments or who initiated cigarette smoking during the study; nonsmokers were youths who reported not smoking at any of the three assessments. Geologists use this type of method all the time to establish relative ages of rocks. But we were hanging out too much, too soon, multiple times a week.

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