IN MANY parts of the world, greasing the palms of corrupt officials is a fact of life. For lorry drivers in poor countries, for example, it can be even more commonplace than paying tolls or taxes. The extortionists are often armed police or soldiers, manning roadblocks, who make little attempt to pretend what they do is legal. Yet, although such people may operate outside the law of the land, they do obey the law of supply and demand.

 See? Clean handsAP

That, at least, is the finding of a recent study* of illicit transactions in Indonesia. In a rare attempt at documenting bribery, it shows how crooked officials act as independent monopolists, maximising their profits and employing sophisticated pricing schemes in ways that have an economic logic, as well as a criminal one.

The authors studied bribes paid by lorry drivers along two main roads in Aceh, an Indonesian province where separatist guerrillas had long been active. Over nine months in 2005 and 2006, data gatherers accompanied the truckers on 304 trips to and from Aceh, recording more than 6,000 illegal pay-offs at military roadblocks, police checkpoints and weigh stations. During the 637-kilometre (396-mile) trip from Medan to Meulaboh, for example, drivers typically passed through 27 checkpoints and forked out a total of $23 in bribes, representing roughly 13% of the cost of their trip—more, even, than the total wages of those in the truck.

In the early stages of each trip, transactions were typically conducted without negotiation—at each stop, drivers simply handed over a few thousand rupiah ($0.50 to $1.00) or a couple of packs of cigarettes. As the trucks neared their destination, however, checkpoint officials demanded increasingly larger sums. At each stop, drivers found themselves with a progressively stronger incentive to avoid hassle and safeguard their cargo, which gave the extortionists greater power over them.

Midway through the study, after the Indonesian government had signed a cease-fire with the rebels, it began a phased withdrawal of 30,000 troops, leading to the number of checkpoints falling by half. This gave the researchers the chance to see how the extortion market would adjust. As you would expect, the amount lost to bribery decreased—but only by 36%.

Fewer stops meant fewer bribes, but this was offset by a rise in the amounts demanded at the remaining checkpoints, whose operators, with entrepreneurial zeal, seized the chance to capture part of the newly liberated surplus. In fact, they behaved just like monopolists, setting their prices so as to maximise their own revenue, without considering the response of the fellow at the next checkpoint, or whether their activities would deter truckers. The result was a textbook example of double marginalisation—when a chain of independent monopolists charges more, but receives less overall than a single monopoly.

These results have intriguing implications for stamping out corruption. In theory, a centralised system of bribery is better for both truckers and extortionists than a string of corrupt officials acting independently. Taking out a kingpin may yield splashy headlines, but it can actually increase the total amount paid in bribes if it destroys co-ordination among his henchmen. A better bet, say the authors, is to reduce the number of troops and police officers. That would, indeed, be a novel way of fighting crime.

* “The Simple Economics of Extortion: Evidence from Trucking in Aceh”, by Benjamin Olken and Patrick Barron.