Consider violent crimes committed by drug gangs. In many cities, such gangs are too numerous for police to watch them all closely. Knowing that they are unlikely to be caught and punished, members can violate the law with impunity. In such situations, Mr. Kleiman argues, the police can gain considerable leverage just by publicizing an enforcement priority list.

Image Credit... David G. Klein

It is an ingenious idea that borrows from game theory and the economics of signaling behavior.

To see how it works, suppose that all drug violence in a city is committed by members of one of six hypothetical gangs  the Reds, Whites, Blues, Browns, Blacks and Greens  and that the authorities have enough staffing to arrest and prosecute offenders in only one gang at any one time. Mr. Kleiman proposes that the police publicly announce that their first priority henceforth will be offenders in one specific gang  say, the Reds (perhaps because its members committed the most serious crimes in the past).

This simple step quickly persuades members of that gang that further offenses will result in swift and sure punishment. And that is enough to deter them.

With the Reds out of action, the police can shift their focus to the Whites. They, too, quickly learn that violent offenses result in swift and certain punishment. So they quiet down as well, freeing the police to focus on the Blues, and so on.

But why don’t the Reds, seeing that the police have moved on, start committing violent offenses again? The reason is that they always remain atop the enforcement priority list. If they start offending again, police attention will again quickly focus entirely on them.

After a few rounds, Mr. Kleiman argues, the Reds will get the point. In like manner, one gang after another is pacified, even though the police have no more resources than before.

Considerable evidence supports Mr. Kleiman’s emphasis on the efficacy of immediate sanctions. Experimenters have found, for example, that even long-term alcoholics become much less likely to drink when they are required to receive a mild electric shock before drinking. Many of these same people were not deterred by their drinking’s devastating, but delayed, consequences for their careers and marriages.