"the law requiring longer sentences has been effective in lowering crime. Within three years, crimes covered by the law fell an estimated 8 percent. Seven years after the law changed, these crimes were down 20 percent."
In recent years, almost every state has adopted some form of "sentence enhancements" as a way to fight crime. These laws come under a variety of names including "three strikes and you're out," determinate sentencing laws, and repeat-offender enhancements. Regardless of the name, they all share one common feature: stiffer punishments for offenders committing the most serious crimes.
In Using Sentence Ehhancements to Distinguish between Deterrence and Incapacitation (NBER Working Paper No. 6484), Daniel Kessler and Steven Levitt analyze the outcome of one such law: California's Proposition 8. Passed by popular referendum in 1982, this law requires courts to lengthen the sentence of repeat offenders in cases of willful homicide, forcible rape, robbery, aggravated assault with a firearm, and burglary of a residence. Kessler and Levitt find that the law requiring longer sentences has been effective in lowering crime. Within three years, crimes covered by the law fell an estimated 8 percent. Seven years after the law changed, these crimes were down 20 percent.
In order to obtain these estimates, the authors collected data on crimes covered by Proposition 8 and on a set of crimes that was exempted from the law (burglary of a non-residence, aggravated assault without a firearm, simple assault, and larceny). By comparing California's crime rates for these two sets of crimes before and after Proposition 8 to rates in the rest of the nation, they can isolate any causal effect of the law change. Prior to the passage of Proposition 8, California's experience with the two sets of crimes mirrored that of the United States as a whole. Immediately after the law changed, crimes covered by Proposition 8 fell in California compared to the rest of the nation. Crimes not eligible under Proposition 8, however, showed no such pattern.
The timing of the declines in crime also sheds light on the reasons why crime fell. The primary effect of Proposition 8 was to increase the sentence length of criminals who would have gone to prison even without the law. Thus, for the first few years after the law changed, it had no impact on the size of the prison population: everyone affected by the law would have been behind bars anyway. The authors argue that the immediate decreases in crime -- roughly half of the overall decline -- therefore must be attributable to deterrence. Criminals, fearing the harsher sentences that awaited them, reduced their illegal activity.
The fact that the impact of the law's change continued to grow steadily over time suggests that incapacitation also helped to reduce crime. Because convicted criminals were serving longer sentences, years after the law's change they were still locked up, rather than out on the streets committing crime.
The results of this study are particularly relevant to the spread of "three-strikes laws" which entail extremely long sentences upon a third conviction of a crime. If criminals are effectively deterred by such laws, then it is possible that both the amount of crime and the number of prisoners can decline. On the other hand, if incapacitation is the only effect, then such laws can lead to the imprisonment of individuals long after their active criminal years are over. Such a geriatric prison population is an extremely inefficient use of resources, since criminal activity declines rapidly as individuals age. The fact that both deterrence and incapacitation play an important role in reducing crime under Proposition 8 suggests that the results of enforcing "three strikes" laws will be neither as successful as supporters of the law argue nor as disastrous as critics have predicted.
As Kessler and Levitt note, "a direct empirical test of three-strikes is not possible because of the failure of states to enforce such drastic laws in spite of having them on the books." Twenty-four states have passed such laws since 1993, but only California has widely applied its statute. Prosecutors and judges are reluctant to use the three-strikes laws when the punishment for a minor offense, say drug possession or a property crime, is so extreme. The authors conclude that sentence enhancements that are broader in scope and less punitive, such as Proposition 8, may ultimately prove more effective in fighting crime than the three-strikes laws since the former are more likely to actually be enforced.