Adolescent smoking and drinking: are they "epidemics"?

During adolescence, cumulative prevalences of ever using alcohol and ever smoking a cigarette increase systematically and dramatically. We applied a statistical theory of the transmission of epidemic infectious disease to model life-time prevalences of smoking and drinking. Alcohol use prevalences fit closely to a logistic curve used to model an epidemic process that assumed adolescents have random contacts with one another each year. An "adequate contact" will convert a nondrinker to drinking status if he/she is contacted; drinkers average .48 adequate contacts per year. Smoking prevalences were fit assuming both that the entire population was "at risk" and that some individuals were "immune": the mean contact parameter was .28 for smoking if no immune class was assumed and .77 if an immune class was assumed. Extensions of these epidemic process models could include individual differences in contact rates and transitions among several smoking or drinking statuses (e.g., non-user, experimenter, regular user and recovered user).