This article appears in the March 19, 2012 issue of National Review.

Perhaps the first and foremost role of the government is to protect its citizens from crime. It can do so by providing active and visible police protections, and by vigorously pursuing and prosecuting criminals once crimes have been committed. There have been many crime-fighting innovations in recent years, and crime rates have fallen sharply at the same time. But there has been little hard evidence that all of the high-tech techniques contributed to the crime reduction. Until now.

One innovation of the past two decades has been the spread of state-maintained databases of criminal offenders' DNA profiles. The databases make it easier for the authorities to find and ultimately capture suspects. In principle, this increased capability could have a chilling effect on crime as potential criminals abandon illegal pursuits in the face of higher odds of conviction. 

"Doleac's results suggest that adopting the U.K. approach would save 415 lives per year. And compared with increasing police forces, expanding a DNA database costs almost nothing." - Kevin A. HassettStanford University economist Jennifer Doleac has written a fascinating new paper that explores the impact on crime of DNA databases. The paper exploits random variation in the timing of database expansions. Different states have different criteria for putting people into their databases, and have often changed those criteria. They typically expand their databases following widely publicized "if only" cases: cases in which terrible crimes could have been prevented if only the database had been more inclusive. For example, California added incarcerated felons to its DNA profiles after it was revealed that a man who was convicted of raping 14 women had served time for a felony burglary years earlier. Had his DNA been in the system after that incarceration, he probably would not have been able to commit so many rapes.

Doleac compares criminals who were released before database expansions took effect with those released afterward. She finds that those in the database are far more likely to be caught if they commit a crime, and far less likely to commit new crimes in the first place.

The scale of her findings is quite striking. The nearby chart shows the results of a simulation based on her evidence. A hypothetical 50 percent increase in average data base size, which in 2008 would have been an increase from about 177 to 266 profiles per 10,000 residents, has a statistically significant effect on crime rates. It would result in a 13.5 percent reduction in murder, a 27.2 percent reduction in rape, a 12.2 percent reduction in aggravated assault, a 12.0 percent reduction in larceny, and a 22.7 percent reduction in vehicle theft, as well as a statistically insignificant (5 percent) reduction in burglary.

While a 50 percent increase might be difficult to achieve without arousing concerns about civil liberties, the U.S. could choose to follow the lead of the United Kingdom, where all arrestees suspected of serious offenses are included in a database. In the U.S., the addition of arrestees for serious felonies would increase the database size by 12 percent, which would still have a significant impact on crime. The FBI's Uniform Crime Reports show that 12,996 murders were committed in the United States in 2010. Doleac's results suggest that adopting the U.K. approach would save 415 lives per year. And compared with increasing police forces, expanding a DNA database costs almost nothing.

DNA databases have significantly increased the safety of our citizens. Policymakers should explore ways to expand them without prompting fears of Big Brother.

Kevin Hassett is a senior fellow and director of economic policy studies at AEI.