Legalizing marijuana for recreational use has had no significant impact on serious crime rates in Colorado or Washington, according to a new study.

Researchers at Washington State University, Stockton University and the University of Utah based their conclusion on a comparison of monthly rates for violent and property crime between 1999 and 2016 in the two states—the first U.S. jurisdictions to decriminalize the possession and sale of cannabis for recreational use—with the crime rates in 21 states where it was illegal.

Although they found an initial but short-lived uptick in some crime categories, the overall serious crime rate in both states was unaffected over the period, the researchers concluded.

“Our results…suggest that legalization has not had major detrimental effects on public safety,” the study said.

The study noted there had been a “significant decline” in property theft in Washington state—although they did not draw a connection with legalization.

The researchers also cautioned that it would be “premature” to suggest that marijuana legalization actually reduced crime—an argument that some proponents used as a rationale for legalizing pot, on the grounds that it would reduce illicit trafficking by crime cartels—noting that “crime is not the only measure of public safety.”

The study, which appears in the latest issue of Justice Quarterly, a publication of the Academy of Criminal Justice Sciences, represents the first evidence-based assessment of the “grand ongoing experiment” underway across the U.S. to decriminalize marijuana, said Ruibin Lee, assistant professor of criminal justice at Stockton University, and the lead author of the study paper.

“Given the likelihood of more states legalizing recreational marijuana, we felt it was important to apply robust empirical methods to parse out the effects of this action on crime in the first years after legalization,” he said in a press released accompanying the paper, distributed by the Crime & Justice Research Alliance.

Voters in Washington and Colorado approved the legalization of recreational pot in 2012. As of June, nine other states and Washington, DC have joined them. Vermont and DC, however, have only decriminalized possession, not sales.

The incidence of other illegal activities that might be attributed to the wider use of pot, such as driving under the influence, were not examined by the researchers, who added that they could not rule out the possibility that legalization might have different impacts on crime rates in specific communities within a state.

Nevertheless, they declared, the overall results are “quite clear” in relation to serious crime.

“The legalization of marijuana has not resulted in a significant upward trend in crime rates,” the researchers wrote, adding, “We observed virtually no statistically significant long-term effects of recreational marijuana legalization or retail sales on violent or property crime rates.”

The full study can be downloaded free for 30 days here, after which it will be available for purchase only.