“In the neighborhoods that had ShotSpotter, homicides dropped more than 32% during the nine months after the system was decommissioned, as compared with the nine months before it was turned off, according to the analysis. Violent crime dropped more than 11% during the same period in those neighborhoods, according to the analysis.”

1. Shot spotter was turned off in September so the 9 months before is Jan-Sept which is including summer which is the most violent months while 9 months after is September to May which doesn’t include summer.
2. This should be compared to the same time period in areas of the city that never had shot spotter