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. 2012 Aug 1;124(3):259-67.
doi: 10.1016/j.drugalcdep.2012.01.020. Epub 2012 Feb 21.

Trends in U.S., past-year marijuana use from 1985 to 2009: an age-period-cohort analysis

Richard Miech  1 , Stephen Koester
Affiliations

Trends in U.S., past-year marijuana use from 1985 to 2009: an age-period-cohort analysis

Richard Miech et al. Drug Alcohol Depend. .

Abstract

Background: We present a formal age-period-cohort analysis to examine if the recent increase in past-year marijuana use among the young is specific to the younger generation or if, instead, it is part of a general increase present across cohorts of all ages. This is the first age-period-cohort analysis of past-year marijuana use that includes adult trends from 2001 to 09.

Methods: Data come from the National Survey on Drug Use and Health, a series of annual, nationally representative, cross-sectional surveys of the U.S. civilian, non-institutionalized population. The analysis focuses on the 25 year time span from 1985 to 2009 and uses the recently developed 'intrinsic estimator' algorithm to estimate independent effects of age, period, and cohort.

Results: The recent increase in past-year marijuana use is not unique to the youngest birth cohorts. An independent, positive influence of cohort membership on past-year marijuana use, net of historical period and age effects, is smaller for today's youngest cohorts than it was for the cohorts that came immediately before, and, in fact, is at its lowest level in three decades. The recent increase in marijuana use among the young is more consistent with a historical period effect that has acted across all cohorts. Period and cohort trends differ substantially for Hispanics.

Conclusions: The major forces that drive trends in past-year marijuana use are moving away from cohort-specific factors and toward broad-based influences that affect cohorts of all ages. Strategic public health and policy efforts aimed at addressing the recent increase in past-year marijuana use should do the same.

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Figures

Figure 1
Figure 1
Observed Prevalence of Past-Year Marijuana Use by Age Groups, Sex, and Survey Year Note: Prevalence estimates in 2002 as compared to previous years are slightly inflated due to a methodological change. In 2002 the National Survey on Drug Use and Health first began offering monetary incentives to respondents for their participation.
Figure 2
Figure 2
Age, Period, and Cohort Effects for Past-Year Marijuana Use for Men and Women, All Race/Ethnicity Groups Combined
Figure 3
Figure 3
Age, Period, and Cohort Effects for Past-Year Marijuana Use by Race and Ethnicity (continues) * note: Analysis excludes Hispanics age 60–64 (and as a consequence not enough information is available to estimate effects for the 1925–29 birth cohort) because model would not converge when they were included in the analysis pool
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