Members of the Dayton Police Department Drug Enforcement Unit walk out of a home that was searched for heroin in 2015 in Dayton, Ohio. (Ty Wright for The Post)
Opinion writer

A new study published in the Proceedings of the National Academy of Sciences has found that there’s little upside to militarized policing. The study looked at data from Maryland, where a state law required that police agencies in the state submit biannual reports on how and how often they used their SWAT teams. The law was in effect from 2010 through 2014, after which the legislature allowed it to expire. Author Jonathan Mummolo performed a statistical analysis of the Maryland data and crime rates, officer safety data, and race.

After controlling for variables such as local crime rates, Mummolo found that for every 10 percent increase in the black population of a given Zip code, there was a 10 percent increase in the likelihood of that Zip code being raided by a SWAT team.

As for public safety, he found an increased likelihood of violent crime in jurisdictions with a SWAT team, although that increase became statistically insignificant over time. He found no statistically significant change in the killings of police officers — which were too infrequent to measure — or assaults on police officers.

Finally, Mummolo looked at how the use of SWAT teams affects public perception of the police with a smart little experiment. In two separate surveys, he showed volunteers a story about a police chief asking for a budget increase. But volunteers got one of four photos with the story. One photo depicted a group of cops in their traditional blue uniforms. The other three depicted various degrees of militarization, culminating with a photo from Ferguson, Mo., of heavily armed officers surrounding an armored vehicle, with a sniper perched on the roof. He then asked the respondents questions about crime and policing.

Militarized images in the M-Turk survey caused clear increases between roughly 8 points and 15 points in perceived levels of crime in the vignette city. The high militarization condition in the SSI survey caused a statistically significant 2.2-point increase in the perceived level of crime in the vignette city and, strikingly, a 3.2-point drop in respondents’ desire for more police patrols in their own neighborhoods.

In other words, people assumed that the place where the militarized cops were policing had higher crime, but the image also made them less trusting of police in general. This is also interesting:

The high militarization treatment also caused support for police funding in the United States to fall by roughly four points in the M-Turk survey and two points in the SSI survey. Support for funding the department in the news article also fell.

Hey, maybe this is the way to bring law enforcement on board with demilitarization.

Though it’s helpful to have this hard statistical analysis, little of this should be surprising. SWAT teams are usually justified with the argument that they’re needed to confront hostage takers, active shooters and other immediate threats to public safety (and situations in which SWAT teams tend to perform well), but in practice they’re mostly used to serve warrants on low-level drug offenders. The Maryland data showed us that 90 percent of SWAT raids in that state were to serve search warrants. Half of those were for nonviolent crimes, with the overwhelming majority of those being drug crimes. About a third of the raids resulted in no arrests.

Utah is the only other state to experiment with requiring police agencies to report on the use of SWAT teams. The first batch of numbers, released in 2015, showed that 83 percent of SWAT deployments were to serve search warrants for drug crimes. Less than 5 percent of deployments were in response to a violent crime in progress. Just three of 559 reported raids — or 0.5 percent — turned up illegal firearms.

Mummolo’s study provides some needed statistical heft in this discussion. But I’m skeptical that it will have much impact with lawmakers. The Maryland data confirmed what critics of the overuse of SWAT teams had been saying for years. It didn’t result in a single restriction or regulation of SWAT teams. Instead, the legislature responded to the figures by allowing the law that provided them to expire (although there has been some progress in Utah). I guess if there’s no data to ignore, you can’t be accused of ignoring the data.