Who Pays for California's 3-Strikes Sentencing Rule? Arizona and Nevada.

There is no question that criminal activity dropped appreciably after California adopted a "three-strikes" mandatory sentencing rule in 1994. A report issued by the state a decade later found crime rates had fallen dramatically across the board.

Similar rules which force judges to hand down longer prison terms once a criminal has committed three or more offenses have been adopted in over 20 states, but California's version is by far the most stringent.

Yet two unintended consequences of the three-strikes law call into question its ultimate effectiveness, says Harvard economist Radha Iyengar.

In a new study looking at criminal activity in California during the 1990's, Iyengar finds that criminals who already had two strikes against them were 10 percent more likely to make the third strike a violent one. That translates into 21,000 additional violent crimes per year, Iyengar estimates.

The reason? It's about bang-for-the-buck.

Three-strikes laws raise the cost of criminal activity, so if you're a criminal with a prior rap sheet, why use your last opportunity on a small-time job like a burglary or theft when you can extract the most "benefit" by committing a more damaging crime like rape and robbery?

More surprisingly, but not illogically, criminals shifted future offenses to other, more lenient states. Iyengar estimates that 50,000 additional crimes were committed outside of California because of its three-strikes rule. Hardest hit by this extra criminal activity were Arizona and Nevada.

Iyengar's results suggest that California's three-strikes rule is pricier than previously calculated. Using an estimate for the cost of crime for victims, she found that the increase in violent acts offset some, but not all, of the gains from the drop in overall criminal activity.

However, "if you include the increased cost to other states, the costs of increasing incarceration and the long-term effects of prison," Iyengar said in an interview, "[the three-strikes rule] becomes less and less effective."

(Image Credit: Lake County Museum/CORBIS)