TO WHOM does the legroom on an aeroplane belong? More specifically, who owns the four inches of knee-space into which a passenger can recline his seat?

The accepted notion is that such territory belongs to the person seated in front. That flyer has, after all, paid for a reclining chair and thus believes it is his “right” to occupy the space behind. If he remains upright, magnanimously bequeathing extra inches to the person behind, it is on the understanding that he can move the border whenever he likes.

But, in common with many borders, disputes are inevitable. Sometimes the newly squished passenger will wage a guerilla war, perhaps by wedging his knees into the back of the seat in front, ensuring that the price of territorial expansion is discomfort. Weapons may also be deployed. The Knee Defender, a device that can be attached to the chair in front to render it rigid, is banned by many airlines, but that does not deter desperate flyers from using them. All too often, real warfare ensues. Witness the brawl on a recent Southwest flight to Burbank, after one flyer accused another of “messing with his chair”.

Would such fights be prevented if ownership of those four inches were up for auction? This was the starting point of an experiment by Christopher Buccafusco and Christopher Jon Sprigman, two law professors, which they have written up on the Evonomics website.

Their aim was to discover whether recliners’ pleasure at being more horizontal is greater than the amount of suffering this inflicts on the person behind. One obvious way to do this is to put a monetary value on it: find out how much the flyer in front would be willing to pay for the right to recline his seat, and compare that with the amount the person behind would be prepared to shell out to stop this from happening.

In an online survey the researchers asked people to imagine that they were about to take a six-hour flight from New York to Los Angeles. Respondents were told that the airline had created a new policy that would allow flyers to pay those seated in front of them not to recline their seats. Some were then asked how much the passenger behind would have to pay them not to recline during the flight. Others had to specify how much they would be prepared to pay to prevent the person in front of them from reclining.

Recliners wanted on average $41 to stay upright, while reclinees were willing to pay only $18 on average. Ownership of the four inches would change hands only 21% of the time. The result suggests that the balance of rights is about right; we are correct to think of that space as belonging to the person in front.

Except that things are not so straightforward. According to the theories of Ronald Coase, who won the Nobel Prize in Economics in 1991, the space between airline seats is a scarce resource. Therefore it should not matter who has the initial ownership (assuming there are no barriers to a deal being made). The market will out: whoever values the space more will buy it from the other. (In this case it would normally revert to the recliner.)

But as the professors explain:

When we flipped the default—that is, when we made the rule that people did not have an automatic right to recline, but would have to negotiate to get it—then people’s values suddenly reversed. Now, recliners were only willing to pay about $12 to recline while reclinees were unwilling to sell their knee room for less than $39. Recliners would have ended up purchasing the right to recline only about 28% of the time—the same right that they valued so highly in the other condition.

In a Coasean world, that makes little sense. But it does when one factors in the work of Daniel Kahneman, perhaps the world’s most famous behavioural economist. Mr Kahneman has shown time and again that ownership does, in fact, matter when striking a deal. According messieurs Buccafusco and Sprigman:

People generally don’t like losing things that they have. When a resource is provided to them as a default—even something as trivial as a pen—people tend to be unwilling to part with it. As a consequence, the least amount of money they are willing to accept to give it up is often much greater than the amount that they would be willing to pay to purchase the same item.

All of which leaves us in a bit of a pickle on how best to avoid future conflict. Perhaps the best solution to this particular border dispute is to create a demilitarised zone. Airlines should simply install non-reclinable seats.