FBI data showed that violent crime increased 4 percent last year, and homicides jumped nearly 11 percent. Yet crime overall went down. The New York Times concludes that “whether crime is up or down depends on what data is being looked at and who is doing the looking.” Criminologists and police officials said the decline in homicides has been so significant in the last quarter century that sudden increases in a few cities can skew the picture. “It isn’t a national trend, it’s a city trend, and it’s not even a city trend, but a problem in certain neighborhoods,” said Richard Berk, a professor of statistics and criminology at the University of Pennsylvania. “Certainly, people around the country should not be worried. People in Chicago shouldn’t be worried. But people in certain neighborhoods might be.”
Explanations for the increase in homicides in some cities are largely guesswork. Criminologists acknowledge that the required analysis has not been done in the neighborhoods where killings are occurring. “Why is there a rise? No one can possibly know that,” said Robert Smith, director of the Fair Punishment Project at Harvard Law School. “But crime statistics are most accurate when they are block by block, because even a neighborhood is too large.” Attempts at explanations are numerous: battles over drug dealing turf; the dissolution of powerful street gangs, resulting in violent crews that disband as quickly as they form; petty disputes that turn deadly because of the availability of guns; and a deepening economic and social isolation of the poorest people.