Fig. 2: Cumulative probability of attaining milestones of onset of cigarette smoking from time since initiation among 311 participants who were nonsmokers at baseline and who initiated cigarette smoking during follow-up. See Methods for definitions of the milestones. *Thirty-six subjects reported mental addiction and 15 reported physical addiction before initiation. These subjects were considered to be incident cases at baseline; they contributed zero person-months to the denominator in the computation of time at risk for selected milestone.