The detailed methodology and findings of our study are included in a legal brief filed on May 3, 2021, in Cook County Circuit Court. The brief was filed on behalf of a coalition of Chicago community organizations in support of a pending challenge to the reliability of ShotSpotter evidence by the Cook County Public Defender. The organizations filing the brief are Brighton Park Neighborhood Council, Lucy Parsons Labs, and Organized Communities Against Deportations.

The raw data on which we relied was obtained through FOIA from the Chicago Office of Emergency Management and Communications. The data was contained in two spreadsheets, one covering the period from July 1, 2019 through December 31, 2019, and another covering January 1, 2020 through April 14, 2021. The latter, more recent dataset was obtained by MJC in partnership with the Invisible Institute.

The disposition codes contained in the spreadsheets were interpreted using the Incident Reporting Guide and Miscellaneous Incident Reporting Guide published by the Chicago Police Department.

The dispatch “type” codes contained in the spreadsheets were interpreted using a document previously obtained from OEMC by the Chicago Justice Project.

There have been other studies of ShotSpotter and similar gunshot detection systems that reached similar conclusions.

The South Side Weekly published a deeply-reported article in 2017 by Michael Wasney that included a careful analysis of ShotSpotter data from Chicago.

Forbes published a study in 2016 by Matt Drange examining data about ShotSpotter-initiated police deployments in seven cities.

A small number of academic studies have been done of ShotSpotter and related acoustic gunshot detection systems. Among the most recent are studies by Doucette et al. (2021) in the Journal of Urban Health, Mares & Blackburn (2020) and Ratcliffe et al. (2018), both published in the Journal of Experimental Criminology.