In order for drinking, problem drinking, the use of
marijuana, the use of pills (amphetamines, barbiturates, or
hallucinogens), and the use of "hard drugs" (cocaine or
heroin) to constitute a unidimensional, cumulative (Guttman)
scale, adolescents who use one of the less widely-used
(more extreme, more "difficult") drugs should report the use
of at least one drug in each of the categories of more popular
drugs as well