Age-period-cohort models of 1984 to 2010 cannabis trends in the US National Alcohol Surveys

Objectives: Studies show cannabis use in the US to be increasing in recent years. Previous research has identified cohorts born after 1945 as having increased cannabis use prevalence and has suggested the importance of period effects in recent increases. Estimated APC effects have also been found to differ between Hispanics and other groups.

Methods: Data from six National Alcohol Surveys are utilized in examining trends in cannabis use prevalence and frequency with attention to relationships with alcohol trends. Building on our earlier study of trends through 2000, we estimate age-period cohort decomposition models for cannabis outcomes controlling for socio-demographic measures. Models are estimated for the population, men, women, African Americans, Hispanics and whites.

Results: Results indicate the importance of both period effects and cohort effects in rising cannabis use prevalence and frequency in the 2010 survey. The addition of alcohol use measures to models is found to reduce estimated cohort effects suggesting an inter-relationship between cohort cannabis and alcohol use. Differences in age, period and cohort effects are found across race/ethnicity groups.

Conclusions: The recent upward trend in cannabis use appears to be related to both period and cohort influences and positively linked to effects for alcohol suggesting the need for both population and cohort–targeted strategies for substance abuse prevention.  Differences in age profiles as well as period and cohort influences across race/ethnicity groups indicates the importance of separate analyses for these groups.