Explaining the Extraordinary Decline in Chicago’s Homicide Arrest Rates, 1965 to 1994 and Beyond: Trends in Case Mix Versus Standards for Arrest

Chicago’s homicide arrest rate dropped from 91% in 1965 to 57% in 1994 and dropped still lower in recent years. This pattern mirrors the trend in the national homicide clearance rate. A plausible explanation for this great decline is the trend in homicide case mix, which arguably has made it intrinsically more difficult to solve homicide cases. Our analysis describes the change in case mix for the period 1965 to 2020 and analyzes the effect on the arrest rate for the first 30 years of this period, all by use of a unique homicide case microdata set. We document the large changes in case mix: for example, the percentage of all homicides in which a male victim was shot outdoors increased from 18% (1965) to 69% (2020). But the change in case mix does not account for Chicago’s great decline during the earlier decades, as we demonstrate by use of a novel arrest rate index. In fact, the arrest rates in each of the categories defined by location, sex, and weapon type exhibited similar declines through 1994. (Subsequent years of arrest data are unavailable for now.) Our preferred explanation for the great decline is that the operational standard for making an arrest increased during this period. That interpretation is well supported by evidence explaining the corresponding national trend, though direct evidence is lacking for Chicago. This interpretation challenges the use of the arrest rate as a police performance indicator and offers a positive interpretation of the great decline.