The prevailing wisdom is that crime rates rise as people get increasingly desperate during tough economic times. But, despite the lingering effects of a recession, the number of violent crimes across the U.S. dropped by 5.5 percent last year — to what might be the lowest rate in nearly 40 years, The New York Times reports. Why? Here, four theories:

1. We're steering people away from crime
These stats "justify both celebration and head-scratching," says Douglas A. Berman at Sentencing Law and Policy. Perhaps the internet is helping law-abiding people identify and avoid dangerous areas. Or maybe programs requiring the registration of sex offenders are really working — and helping to prevent some sex-related crimes.

2. We're getting better at identifying would-be criminals
Improved success at diagnosing and medicating kids with emotional or psychological problems could also be a factor, says Berman. Sussing out those issues early in life may help problem children avoid becoming "crime-prone adults." 

3. Tough times don't actually cause crime waves
Intellectuals love to argue that money trouble turns people bad, says Tyler Cowen at Marginal Revolution, but that doesn't make it true. People perpetuate this fallacy whenever they want to bolster their proposals on financial or social policy, using the threat of potential mayhem, should the other side prevail.

4. Crime actually isn't down across the board
If you live in New York City, this debate makes no sense, says Adam Martin at The Atlantic Wire. NYC's murder rate  climbed by 14 percent, and Boston, too, saw "an extremely sharp rise in the murder rate." San Antonio, like New York, saw its overall crime rate go up. Granted, these local stats don't overshadow the nationwide trend, but they are "very glaring exceptions" that complicate the effort to draw any fast conclusions.