The research emerging from the Add Health survey strongly indicates that whether or not a teenager has ever had sexual intercourse is largely explained by that individual's own sexual history and his or her own perceptions about the costs and benefits of having sex. This stands in stark contrast to other major risk behaviors--such as cigarette smoking, drug and alcohol use, weapons-related violence, and suicidal thoughts and attempts--which the data indicate are shaped by more generic or external factors, such as frequent problems with school or work, frequency of "just hanging out with friends" and the number of friends who regularly smoke or drink.