The study by Harrison et al. is memorably large: 74,008 students adequately completed questionnaires. Such size creates considerable power, even if limitations include shallowness, even some narrowness, behavioral focus, blending of different categories (use of all substances was blended into generic "substance" use), reliance on questionnaires, and reliance on self-reporting in teenagers (in a realm where self-delusion, peer pressure, wishes to conform, wariness of adult truth-seeking, etc., are not unlikely to create systematic distortions). The authors do consider some important differences between teens and adults as well as other limitations of their survey (e.g., the self-report problems and the fact that the most serious substance abusers may have been left out). Even if the bits of data are imperfect, however, such large studies retain significant strength. Apparently ignoring caffeine and nicotine (alas), the authors offer as one conclusion that alcohol is by far the most common substance used by high schoolers, with marijuana a very distant second. Another conclusion may have enough clout to change something: the authors found that DSM-IV's adult-derived criteria for substance abuse and substance dependence are probably less useful, at least for teenagers, than would be the simpler spectrum of criteria and total number of symptoms they propose.