Age, period, and cohort effects in marijuana and alcohol incidence: UnitedStates females and males, 1961-1990

Using multiple classification models applied to self-report data on initiat ion of drug use from nine National Household Surveys on Drug Abuse conducte d between 1982 and 1995, this paper shows that the directions of change in period and cohort effects were similar for marijuana and alcohol and for ma les and females. Period effects-indicative and societal tolerance or suppor t for drug use during 5-year periods between 1961 and 1990-declined between the early 1970s and late 1980s, while cohort effects-indicative of early e xperiences of birth cohorts favoring drug use-increased. One interpretation is that trends in incidence were determined by two opposing vectors of soc ial forces: Beginning in the 1970s, changes in social policies, values, and drug markets-as reflected in period effects-increasingly acted to reduce i ncidence, while changes in conditions of childhood socialization-as reflect ed in cohort effects-increasingly facilitated or encouraged incidence. Espe cially for marijuana, the increase in cohort effects is larger among female s, which fives rise to Sender convergence-approximately equal male and fema le incidence rates for both drugs-by the late 1980s. An innovative method o f the paper is the adjustment of incidence rates for reporting bias. [Trans lations are provided in the International Abstracts Section of this issue.]