Harvard scholar Radha Iyengar used the "sheep/lamb" metaphor in the title to her abstract of research into California’s "Three Strikes and You’re Out " law .

I visited California in 2004 to talk to experts when studying the dramatic drop in crime in the US since President Clinton’s 1996 reforms. Among them were James Q. Wilson (the professor whose philosophical work inspired and explained the success of New York’s Broken Windows (zero tolerance) changes), and the Rand Corporation scholar who was in charge of the analysis that California law required before the three strikes proposition went on the ballot.

They told me that they had not favoured that kind of mandatory sentencing reform when it was approved by the citizens.They thought nevertheless that it had been much more effective than expected. They remained concerned that too much of its cost was unnecessary.

New Zealand critics usually vent elite confidence that criminals are too dumb to think about punishment risks when deciding whether or not to commit their next crime. "Deterrence doesn’t work". they assert, choosing not to look at the research which has discredited that notion.

I recently came across Iyengar’s interesting confirmation of ‘Three Strikes" powerful deterrent effect, in research that nevertheless suggests some undesired consequences. The research abstract says:

Strong sentences are common "tough on crime" tools used to reduce the incentives for individuals to participate in criminal activity. However, the design of such policies often ignores other margins along which individuals interested in participating in crime may adjust.

I use California’s Three Strikes law to identify several effects of a large increase in the penalty for a broad set of crimes. Using criminal records data, I estimate that Three Strikes reduced participation in criminal activity by 20 percent for second-strike eligible offenders and a 28 percent decline for third-strike eligible offenders.

However, I find two unintended consequences of the law. First, because Three Strikes flattened the penalty gradient with respect to severity, criminals were more likely to commit more violent crimes. Among third-strike eligible offenders, the probability of committing violent crimes increased by 9 percentage points. Second, because California’s law was more harsh than the laws of other nearby states, Three Strikes had a "beggar-thy-neighbor" effect increasing the migration of criminals with second and third-strike eligibility to commit crimes in neighboring states.

The high cost of incarceration combined with the high cost of violent crime relative to non-violent crime implies that Three Strikes may not be a cost-effective means of reducing crime.

Because the research report is available only on subscription here is a link to the Slate summary of the study.