The number of violent crimes in the United States dropped significantly last year, to what appeared to be the lowest rate in nearly 40 years, a development that was considered puzzling partly because it ran counter to the prevailing expectation that crime would increase during a recession. In all regions, the country appears to be safer. The odds of being murdered or robbed are now less than half of what they were in the early 1990s, when violent crime peaked in the United States. Small towns, especially, are seeing far fewer murders: In cities with populations under 10,000, the number plunged by more than 25 percent last year.
The news was not as positive in New York City, however. After leading a long decline in crime rates, the city saw increases in all four types of violent lawbreaking — murder, rape, robbery and aggravated assault — including a nearly 14 percent rise in murders. But data from the past few months suggest the city’s upward trend may have slowed or stopped.
Nationally, the drop in violent crime not only calls into question the theory that crime rates are closely correlated with economic hardship, but another argument as well, said Frank E. Zimring, a law professor at the University of California, Berkeley.
As the percentage of people behind bars has decreased in the past few years, violent crime rates have fallen as well. For those who believed that higher incarceration rates inevitably led to less crime, “this would also be the last time to expect a crime decline,” he said.
“The last three years have been a contrarian’s delight — just when you expect the bananas to hit the fan,” said Mr. Zimring, a visiting law professor at New York University and the author of a coming book on the decline in the city’s crime rate.
But he said there was no way to know why — at least not yet.
“The only thing that is reassuring being in a room full of crime experts now is that they are as puzzled as I am,” he said.