Marijuana Legalization Allowed Police to Better Solve Other Cases, Criminology Study Finds

By Valli Herman

In the states where cannabis legalization measures appeared on ballots, voters were unvaryingly presented with a simple rationale: Legalizing marijuana for all uses will free up police to combat more serious crimes.

There was one problem: The research was scant.

A new study released in the peer-reviewed criminology journal Police Quarterly on July 4, 2018, is among the first in the post-prohibition era to add evidence to that legalization argument, a boon for advocates and police departments hampered by limited resources.

The study, lead by David A. Makin, an assistant professor of Washington State University’s Department of Criminal Justice and Criminology, looked at what authorities call clearance rates to judge police efficiency. Those rates are “the ratio between the number of crimes solved and the total number of crimes recorded by the police,” the report said.

Even though legalization is fairly new, the data suggested that crime clearance rates were increasing more rapidly in states that legalized marijuana, and especially in Colorado.

“Our models show no negative effects of legalization and, instead, indicate that crime clearance rates for at least some types of crime are increasing faster in states that legalized than in those that did not,” the study said.

The most dramatic change was reflected in the steep and immediate drop in arrests for marijuana possession after legalization in late 2012.  Most of the improvements in other types of crime were incremental, with changes of 1 to 2 percent, Makin told

“People tend to focus so much on percentages. When you are dealing with the volume of crimes that states report, when you look at a 1 percent change, that is really a large number of offenders being apprehended,” he said.

The overall trend is encouraging, however.

Figure 1. Marijuana possession arrest rate, police agencies reporting drug arrests all 12 years
from 2004 to 2015, Colorado, Washington, and states outside the Pacific census region.
Includes 86 Colorado police agencies (serving 79.7% of the state’s 2015 population), 131
Washington police agencies (serving 57.8% of the state’s 2015 population), and 6,242 police
agencies outside of the Pacific region (serving 56.6% of the population) that reported drug
arrests for all 12 years.

“Specific to public safety, advocates of legalization expected improvements in police effectiveness through the reduction in police time and attention to cannabis offenses, thus allowing them to reallocate resources to more serious offenses,” the study said.

Those offenses included rape, robbery, aggravated assault, burglary, larceny and motor vehicle theft. The authors found statistically significant improvements in clearance rates for those and other crimes.



Though prior studies have looked at the impact of laws that moved cannabis possession cases to a lower priority, “few studies have been able to examine the relationship between substantial policy changes and the potential for agencies to reallocate resources” across entire states, the study said.

The sudden switch to legalization represent the kind of substantial policy changes that researchers had long hoped to study. Not since the repeal of alcohol prohibition in 1933 has there been a situation that mirrors the sudden changes that occurred in Colorado and Washington, according to Makin.



The study used the FBI’s monthly Uniform Crime Reports data from 2010 to 2015, a date range that spans several years before and after the 2012 legalization votes. When the data is charted on graphs, the pivotal policy change is reflected along the timeline neatly at 2012.

“There is an opportunity cost to every activity an officer engages in,” Makin said. “Marijuana arrests can take hours of time. When it’s legal, you no longer have to expend those hours. The data seem to suggest that this is what has occurred.”

There is more to research, more to learn, particularly in the realms of public health and safety, Makin said.

“We will continue to work diligently until we can say unequivocally and empirically that [legalization]has had an impact in public safety,” Makin said. “We are years away from that.”



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