* No more than 25% of calls to police are about crimes, and many of those turn out not to involve crimes upon the arrival of police at the scene. Closer to 7-10% of calls involve actual crimes. Frequently police restore order when a situation that might escalate to a crime results in a call.
* Only about 13% of reported crimes are violent crimes.
* Most reported crimes are cold by the time police arrive.
* In 1990, the average U.S. police officer made 19 arrests per year.
* About 15% of police resources are devoted to investigating crimes.
* The vast majority of crimes are not solved; in those that are solved a suspect is usually quickly determined on the basis of interview with physical evidence only rarely pointing to a suspect as opposed to confirming the guilt of, or exonerating a suspect from guilty. Most suspects confess.
* A large share of burglaries are solved through confessions by burglars caught in another burglary.
* Detectives spend half an hour on paperwork for each hour spent talking to people and looking for evidence.
* About 7% of police resources are devoted to traffic control (third after investigating crime which is second, and general patrol and response to calls, which is the main activity of police). These three activities account for about 85% of police resources and another 9% or so is consumed by adminstrative duties.
From "Policing" by Tim Newburn (2004) quoting at length from "Police For the Future" by David Bayley (1994).