Economists and bounty hunters would appear to have little in common. Duane “Dog” Chapman is a tattooed ex-convict with his own reality television show, currently threatened with extradition to Mexico for apprehending a US rapist there. Alex Tabarrok wears Gap khaki shorts and is interested in tort reform. Only one of them is an economist.

Nevertheless, there is an unlikely alliance here. Professor Tabarrok and his colleague Eric Helland have been sounding the charge for bounty hunters such as “Dog” - as well as the more traditional kind, who catch fugitives by sweet-talking their mothers or waiting patiently across the street from their girlfriends’ houses. Economists are taking an interest because the bounty hunters are an unusual example of performance-based pay.

A tough question for any legal system is whether suspects should be imprisoned while awaiting trial. Let them out and they may abscond or show up at the mall with a machinegun. Keep them in and you are incarcerating someone who has not been convicted of any crime. There is no easy answer, but an economist’s instinct would be that if you pay judges to get the answer right, they will.

Steven Landsburg, an economist at the University of Rochester, has suggested one way of doing that. A judge would get a fat bonus for every suspect he released, and a stiff financial penalty if the suspect machinegunned anyone. The fatter the bonus, the more the judge will want to risk releasing subjects, and the more the system will favour liberty over public safety. Whether the bonus is small or large, however, the judge has a strong financial incentive to think carefully about which suspects are worth the risk to society - and his bank account.

But what Professor Landsburg may not have realised is that his wacky-sounding idea is already used in most states in America, albeit in a disguised form. Instead of putting the judges on an incentive system, those states have replaced the difficult part of their job with a private judiciary - bail dealers, who have almost exactly the incentives Landsburg advocates.

Under the current system, many suspects are offered bail, which should partly resolve the dilemma between liberty and public safety by allowing a suspect his freedom while giving him a strong reason to return and stand trial. The problem, of course, is that many suspected criminals do not have enough cash to pay for meaningful bail.

This is where bail dealers come in. The bail dealer posts the entire bail bond and takes a 10 per cent fee from the suspect or his loved ones. As long as the suspect shows up in court, the bail dealer gets her bond back and keeps the fee for her trouble (or his trouble - but bail dealers are often women). If the suspect doesn’t show up the dealer hires a bounty hunter to go and fetch him. The bail dealer makes money only if she hardly ever makes the wrong call.

The system is therefore a natural test of whether this sort of unlikely performance pay works. Tabarrok and Helland studied the matter (research methods included data-crunching but also dawn raids around Baltimore), comparing thousands of pairs of suspects with similar backgrounds accused of the same crime.

Those who go through the bail-bond system are more likely to show up in court and more likely to be caught by the likes of “Dog” Chapman if they abscond. Overall they are three times less likely to be successful fugitives, even given the fact that official judges get “first pick” of those who are imprisoned.

What’s next? “Dog” found success after spending time in prison for murder; he calls himself “what rehabilitation stands for”. So why not introduce performance pay for private rehabilitation specialists too?