Impact Of Marijuana Legalization On Crime Reduction Is Being Underestimated, New Study Finds

Studies have repeatedly identified an association between the legalizing marijuana and reductions in crime—but the impact of the policy change is being significantly understated because of limitations in the research methodology, a new paper co-authored by a federal official asserts.

Most studies looking at crime and cannabis rely on FBI data sourced from local police departments across the country. But reporting that data to the federal agency is entirely voluntary, leaving knowledge gaps that have underplayed the extent to which legalizing medical cannabis reduces violent and property crime.

That’s according to researchers from the U.S. Department of Agriculture’s (USDA) Economic Research Service and Appalachian State University, who published a working paper with their findings this month.

“U.S. drug policy presumes prohibition reduces crime. Recently states have enacted medical marijuana laws creating a natural experiment to test this hypothesis but is impeded by severe measurement error with available data,” the abstract states.

To account for those shortcomings, the researchers developed “a novel imputation procedure to reduce measurement error bias and estimate significant reductions in violent and property crime rates, with heterogeneous effects across and within states and types of crime, contradicting drug prohibition policy.”

“We demonstrate uncorrected measurement error or assuming homogeneous policy effects leads to underestimation of crime reduction from ending marijuana prohibition,” the authors said in the paper, which is titled, “Smoke and Fears: The Effects of Marijuana Prohibition on Crime.”

To improve upon existing research, the study authors said they used a “multiple imputation procedure for agency-level crime data to fill in the gaps in the [Uniform Crime Reporting] data that accounts for the inherent uncertainty in these imputed values in the subsequent statistical analysis.”

“Our results indicate that [medical marijuana laws] result in significant reductions in both violent and property crime rates, with larger effects in Mexican border states,” they wrote. “While these results for violent crime rates are consistent with previously reported evidence, we are the first paper to report such an effect on property crime as well. Moreover, the estimated effects of MMLs on property crime rates are substantially larger, which is not surprising given property crimes are more prevalent.”

While the study specifies that the USDA’s official’s involvement in the study “should not be construed to represent” the government’s position on the issue, it’s notable that an agency representative even participated and effectively reached the conclusion that the theory that criminalizing drugs—as the federal government has done for decades—reduces crime seems to be unfounded.

Other data has similarly challenged the notion that prohibition reduces crime.

In 2020, researchers looked at how adult-use marijuana legalization in Washington and Colorado affected crime rates in neighboring states, and the resulting study determined that passage of recreational cannabis laws may have actually reduced certain major crimes in nearby jurisdictions.

The previous year, a federally funded study found that legalizing marijuana has little to no impact on rates of violent or property crime. The policy change did seem connected to a long-term decline in burglaries in one state, however.

A 2018 study from the think tank RAND said county-level data from California suggested that there was “no relationship between county laws that legally permit dispensaries and reported violent crime,” the researchers wrote. What’s more, there was a “negative and significant relationship between dispensary allowances and property crime rates,” though it’s possible that’s the product of “pre-existing trends.”

That same year, researchers at Victoria University of Wellington and Harvard University found that medical marijuana laws essentially have a null effect of crime rates, with one big exception: A nearly 20 percent reduction in violent and property crimes in California following the legalization of medical cannabis there.

DEA marijuana seizures have significantly declined as more states have moved to legalize cannabis, a new study led by a top marijuana investigator for the federal government found. And at the same time, marijuana arrests are also dropping across the country, and they dipped significantly in 2020, recent FBI data shows.

Federal marijuana trafficking cases also continued to decline in 2020 as more states have moved to legalize, an analysis from the U.S. Sentencing Commission (USSC) that was released in June found.

Federal prosecutions of drug-related crimes overall increased in 2019, but cases involving marijuana dropped by more than a quarter, according to a report released by Supreme Court Chief Justice John Roberts that year.

A study released by the Cato Institute in 2018 found that “state-level marijuana legalization has significantly undercut marijuana smuggling.”

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