Methodological Considerations when Comparing the Effects and Impact of Marijuana Laws across States

Issues:  Changes to state-level marijuana laws have increased considerably over the past decade yet little is known as to whether such laws have an impact on marijuana use. To date, studies have investigated whether differences or changes in decriminalization or medical marijuana laws result in changes in use, however this research is inconclusive and results are often mixed.

Description: There are several potential reasons why studies examining state marijuana laws and their impact on use are inconclusive, such as the variability of state marijuana laws, study design, and measurement considerations.

Lessons Learned: A key issue when investigating whether differences or changes in state marijuana laws impact use is the variability of state laws. Possessing a small amount of marijuana in one state with “decriminalization” laws may lead to no penalties or fines (e.g., Alaska), while in another, it may lead to being charged with a misdemeanor and being fined up to $650 (e.g., Oregon). Examining laws in a dichotomous manner (e.g., criminalization vs. decriminalization) does not adequately capture such differences. Additionally, study design and measurement issues such as temporal sequencing, length of study, period effects, cohort effects, and age effects are important considerations. Finally, confounding variables affecting community- or state-level norms, use of self-report data, differing enforcement practices, and other policy considerations (e.g., stop and frisk) must be taken into account.

Recommendations:  Researchers comparing state-level marijuana use rates based on differing or changing marijuana laws must consider many factors such as variability in laws, temporality, measurement, and study design.