(ISNS) -- In the last 15 years, something dramatic has happened in New York City: the crime rate has dropped precipitously, making the city -- where crime once was of epic proportions -- the safest major city in America.

How that happened is a matter of considerable controversy, with popular theories ranging from fiercer policing, to abortion, lead paint, and computer-assisted crime prevention programs.

David Greenberg, a sociologist at New York University, believes none of the theories stand up on their own. It could be all or none of the above, he said.

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