“Police performance in solving crimes is generally measured through clearance rates, a metric defined by the FBI’s Uniform Crime Reports as the proportion of crimes that have had at least one person arrested, charged with the commission of the offense, and turned over to the court for prosecution. Crimes can also be cleared through a variety of exceptional circumstances, such as the confession of a suspect already in custody, the issuance of an arrest warrant for a suspect who dies before apprehension, and other means.” - Anthony Braga, Improving Police Clearance Rates of Shootings: A Review of the Evidence, July 2021
The clearance rate for violent and property crimes has been stagnant in the US for the past 50 years, hovering around 46% and 17%, respectively, during 1971–2019. As follows:
Yet during the same period, crime rates have gone up, then down, now back up again. Does that mean clearance rates have no impact on crime rates? Of course not, though there may be diminishing returns after a certain clearance level has been reached. Obviously if offenders were never arrested, crime would go up. So there’s gotta be a minimum at which the risk of getting caught is high enough to deter criminal behavior. It’s also likely that high arrest rates would have a deterrence effect. But the US has had mediocre clearance rates for a long time.
We might learn more about the effect of clearance rates on crime by comparing the rates of US cities, for instance New York City and San Francisco:
What is wrong with San Francisco? Why such low crime clearance rates? I don’t know. But I do know that SF has one of the highest property crime rates in the nation*. There’s got to be a connection.
—
* “In 2020, San Francisco was in the top three cities with the highest property crime, with more than 4,400 incidents of property crime per 100,000 residents.” –San Francisco Chronicle, November 5, 2022
Reference:
Braga, Anthony A. Improving Police Clearance Rates of Shootings: A Review of the Evidence, Manhattan Institute, July 2021.