How can DNA databases reduce the costs of law enforcement? originally appeared on Quora, the place to gain and share knowledge, empowering people to learn from others and better understand the world. You can follow Quora on Twitter, Facebook, and Google Plus.

DNA databases make it easier for law enforcement to identify offenders in unsolved cases. They work by comparing DNA profiles from known offenders with DNA profiles from crime scene evidence. When a match is made, it is sent to the local law enforcement agency in the hopes that it could point them to a suspect in the case.

This increases the probability that repeat offenders are caught for their crimes. This could (1) take serial offenders off the street more quickly, and (2) deter some individuals who are in the database from reoffending.

My research shows that DNA databases have a big deterrent effect: In the United States, DNA profiling makes violent offenders 17% less likely to reoffend, and makes property offenders 6% less likely to reoffend. (I determine this by comparing individuals released just after database expansions with those released just before. The two groups are nearly identical and subject to all the same criminal justice policies and practices, except that those released just after the expansion are far more like to be added to the database.)

I also show that adding offenders to state databases reduces crime rates, and that this is far more cost-effective than traditional crime-reduction methods like hiring police officers or putting people in prison.

What can we learn from this example? There are two reasons DNA databases are so cost-effective: (1) They increase the probability of getting caught, rather than the punishment. Criminal offenders tend not to be a forward-looking group, and so changing the probability of getting caught is much more effective than adding years to an already-lengthy sentence would be. (2) It is highly scalable. Building labs and computer infrastructure is expensive, but adding an additional offender to an existing database is cheap — and getting cheaper! Rapid DNA machines make quick work of this process, with minimal involvement from lab personnel.

DNA databases may also increase the accuracy of arrests and convictions. To the extent that this reduces the harm done to innocent individuals, that is also a big reduction in the social costs of law enforcement!

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