Mayor says study proves police respond faster without ShotSpotter. The study excluded gunfire calls.

Mayor Brandon Johnson Defends Decision to Disconnect Gunfire Detection Network

Mayor Brandon Johnson on Wednesday once again defended his decision to disconnect the city’s gunfire detection network, claiming that a University of Chicago study found CPD responded “four times faster to the city’s most serious 911 calls” in some South and West Side neighborhoods after the city ended its relationship with ShotSpotter. But that is not what the study says.

The report, which consists of map graphics rather than a detailed analysis, claims police response times improved by four minutes within 12 neighborhoods during the first six months after ShotSpotter was turned off, not that officers responded four times faster. The findings also show that response times improved across most parts of the city during those six months, even in neighborhoods that never had ShotSpotter.

After WTTW published a friendly report about the analysis shortly before Johnson’s press conference, several questions arose about its findings.

One major question is the reliability of the city’s response time data, on which the entire study is built. In September 2023, just months before the study period began, the city’s Office of Inspector General issued a report finding “CPD’s data collection of 911 response times is incomplete.” Notably, WTTW itself highlighted the problem in a story headlined, “Chicago Police Didn’t Track How Long It Takes Officers to Respond to Half of 911 Calls: Watchdog.”

Both the OIG and WTTW reports said the city hoped a new police dispatch system would resolve the issue of poorly recorded response times. But sources within the Office of Emergency Management and Communications, which handles dispatching for CPD, told CWB Chicago that the dispatch system still has not been rolled out.

“Contract was signed in 2020. Rollout was scheduled in 2023. It’s now 2026 and we still aren’t using it,” one OEMC employee said, calling it a “$75 million waste.”

There are also questions about what the U of C researchers actually measured.

Robert Vargas, a sociology professor who leads the UChicago Justice Project, told CWB Chicago the study “was motivated by a specific set of claims made by elected officials that decommissioning ShotSpotter would have serious consequences for police response times.”

However, Vargas also acknowledged that before analyzing response times, his students removed all 911 calls involving shots fired from the city’s dataset. In other words, the study’s conclusions about faster response times, if accurate, did not include gunfire calls, the only type of emergency ShotSpotter was designed to address and the specific response times elected officials had been discussing.

So while the project was “motivated by a specific set of claims made by elected officials,” the analysis itself did not determine whether those concerns about gunfire response times were valid.

There are also questions about the time periods studied. Vargas’ team compared response times from March 2024 through September 2024, when ShotSpotter was disconnected, with the six months afterward.

The concern is that the “before” period included spring and summer months — when 911 call volumes were heavy and neighborhood patrol officers were diverted to the Democratic National Convention, festivals, and other large events — while the “after” period covered fall and winter months, when call volumes were lighter, and officers were back on local patrol.

Vargas said the researchers’ models “included month fixed effects,” but he declined a request to provide the city’s raw dataset, saying his students “don’t want to be scooped on other things they’re using it for.”

Ralph Clark, CEO of SoundThinking, ShotSpotter’s parent company, criticized the UChicago analysis on Twitter, noting it was not peer-reviewed. He also pointed to five peer-reviewed studies that concluded the gunfire detection system improves police response times to shooting incidents.

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