Trading kidneys, repugnant markets and stable marriages win the Nobel Prize in Economics

Roth and Shapley charted a course for economists to go beyond simply arguing for markets in everything.

The 2012 Nobel Prize in Economics - technically the Sveriges Riksbank Prize in Economic Sciences in Memory of Alfred Nobel, but nobody cares - has been awarded to two American Economists, Alvin Roth and Lloyd Shapley "for the theory of stable allocations and the practice of market design". The Nobel Committee explains what that means:

This year's Prize concerns a central economic problem: how to match different agents as well as possible. For example, students have to be matched with schools, and donors of human organs with patients in need of a transplant. How can such matching be accomplished as efficiently as possible? What methods are beneficial to what groups? The prize rewards two scholars who have answered these questions on a journey from abstract theory on stable allocations to practical design of market institutions.

Lloyd Shapley used so-called cooperative game theory to study and compare different matching methods. A key issue is to ensure that a matching is stable in the sense that two agents cannot be found who would prefer each other over their current counterparts. Shapley and his colleagues derived specific methods – in particular, the so-called Gale-Shapley algorithm – that always ensure a stable matching. These methods also limit agents' motives for manipulating the matching process. Shapley was able to show how the specific design of a method may systematically benefit one or the other side of the market.

Alvin Roth recognized that Shapley's theoretical results could clarify the functioning of important markets in practice. In a series of empirical studies, Roth and his colleagues demonstrated that stability is the key to understanding the success of particular market institutions. Roth was later able to substantiate this conclusion in systematic laboratory experiments. He also helped redesign existing institutions for matching new doctors with hospitals, students with schools, and organ donors with patients. These reforms are all based on the Gale-Shapley algorithm, along with modifications that take into account specific circumstances and ethical restrictions, such as the preclusion of side payments.

Even though these two researchers worked independently of one another, the combination of Shapley's basic theory and Roth's empirical investigations, experiments and practical design has generated a flourishing field of research and improved the performance of many markets. This year's prize is awarded for an outstanding example of economic engineering.

The committee have yet again reaffirmed the old adage that the most important thing to do when trying for a nobel prize is to live long enough that your achievements are recognised. The Gale-Shapley algorithm, for instance, was devised in 1962, when Lloyd Shapley was 34. It concerns a maths problem known as the stable marriage problem: if you have an even number of men and women, can you always come up with a set of marriages where there are no two people of opposite sex who would both rather have each other than their current partners? (1960s maths problems: usually heteronormative.) If you can, then the marriage is "stable".

The Gale-Shapley algorithm is a way of always ensuring stable matches; and much of Shapley's work covers the same areas, straddling the boundaries between economics, mathematics, and computer science.

Roth is the younger of the two winners, and works in a far more empirical sphere. As the committee points out, although the two men never actually collaberated, Roth took Shapley's theoretical work and applied it to actually existing markets. For instance, Roth used the Gale-Shapley agorithm to ease the kidney shortage in the US. David Wessel explains (£):

As of noon yesterday, 58,470 people in the U.S. were waiting for a kidney transplant. Most won't get one this year. There aren't enough donated kidneys to go around. Surgeons transplanted just 15,129 kidneys last year. Now a band of transplant surgeons and economists are trying to fix that by creating a moneyless market for exchanging kidneys. Most transplanted kidneys come from a person who has died, a supply that grows slowly because of ignorance about the need for donations or grieving relatives' reluctance. But a kidney taken from a live donor works better, and almost everyone has a spare. As techniques improve for removing healthy kidneys and for suppressing the body's tendency to reject a transplant, doctors increasingly turn to kidneys from living donors, usually relatives. Last year, 43% of kidneys transplanted in the U.S. came from living donors, up from 28% a decade ago. But a biological barrier often blocks a transplant from a relative. In about a third of all would-be pairs, blood types are incompatible. In others, the sick person has antibodies that can initiate a rejection of the donated organ. It's heartbreaking "to have the treasure of the live donor and then have that not go forward because of a biological obstacle," says Massachusetts General Hospital transplant surgeon Francis DelMonico.

Occasionally, transplant centers spot a way out: One New England father with blood type A couldn't donate a kidney to his daughter with blood type B. So he gave a kidney to a teenager with blood type A, and the teenager's sister gave a kidney for the man's daughter. New England's transplant centers have done six such exchanges. Baltimore's Johns Hopkins University has done seven.

The crucial thing about Roth's work, from an economic point of view, is that it involves finding stable allocations using market-like situations without involving money. The kidney swaps in the New England situation are market-like, trading kidneys for kidneys in a way that makes all parties better-off, but they don't actually require kidneys to be bought and sold.

We can see the importance of this by looking at another paper of Roth's, not cited by the committee, on repugnance in markets (pdf). Roth demonstrates that some markets are limited because the very existance of a market in some goods is considered repugnant. He argues, for instance, that the trade in horse meat being banned in California is not done through fears that eating horse meat is unsafe; nor is it done for animal welfare reasons, since it is still legal to farm and kill horses. But banned it is, and Roth argues that the natural response of economists to situations of this type - to argue for freer markets - is wrong, since it ignores the very strong feelings involved in the situation. Instead:

Being aware of the sources of repugnance can only help make such discussions more productive, not least because it can help separate the issues that are fundamentally empirical—like the degree of crowding out of altruistic donations that might result from different incentive schemes compared to how much new supply might be produced—from areas of disagreement that are not primarily empirical.

Hopefully his new Nobel Prize should give that argument greater weight in the years ahead.

A patient receives a kidney in Johns Hopkins university in Baltimore. Photograph: Getty Images

Alex Hern is a technology reporter for the Guardian. He was formerly staff writer at the New Statesman. You should follow Alex on Twitter.

Photo: Getty Images
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No, IDS, welfare isn't a path to wealth. Quite the opposite, in fact

Far from being a lifestyle choice, welfare is all too often a struggle for survival.

Iain Duncan Smith really is the gift that keeps on giving. You get one bile-filled giftbag of small-minded, hypocritical nastiness and, just when you think it has no more pain to inflict, off comes another ghastly layer of wrapping paper and out oozes some more. He is a game of Pass the Parcel for people who hate humanity.
For reasons beyond current understanding, the Conservative party not only let him have his own department but set him loose on a stage at their conference, despite the fact that there was both a microphone and an audience and that people might hear and report on what he was going to say. It’s almost like they don’t care that the man in charge of the benefits system displays a fundamental - and, dare I say, deliberate - misunderstanding of what that system is for.
IDS took to the stage to tell the disabled people of Britain - or as he likes to think of us, the not “normal” people of Britain -  “We won’t lift you out of poverty by simply transferring taxpayers’ money to you. With our help, you’ll work your way out of poverty.” It really is fascinating that he was allowed to make such an important speech on Opposite Day.
Iain Duncan Smith is a man possessed by the concept of work. That’s why he put in so many hours and Universal Credit was such a roaring success. Work, when available and suitable and accessible, is a wonderful thing, but for those unable to access it, the welfare system is a crucial safety net that keeps them from becoming totally impoverished.
Benefits absolutely should be the route out of poverty. They are the essential buffer between people and penury. Iain Duncan Smith speaks as though there is a weekly rollover on them, building and building until claimants can skip into the kind of mansion he lives in. They are not that. They are a small stipend to keep body and soul together.
Benefits shouldn’t be a route to wealth and DWP cuts have ensured that, but the notion that we should leave people in poverty astounds me. The people who rely on benefits don’t see it as a quick buck, an easy income. We cannot be the kind of society who is content to leave people destitute because they are unable to work, through long-term illness or short-term job-seeking. Without benefits, people are literally starving. People don’t go to food banks because Waitrose are out of asparagus. They go because the government has snipped away at their benefits until they have become too poor to feed themselves.
The utter hypocrisy of telling disabled people to work themselves out of poverty while cutting Access to Work is so audacious as to be almost impressive. IDS suggests that suitable jobs for disabled workers are constantly popping out of the ground like daisies, despite the fact that his own government closed 36 Remploy factories. If he wants people to work their way out of poverty, he has make it very easy to find that work.
His speech was riddled with odious little snippets digging at those who rely on his department. No one is “simply transferring taxpayers’ money” to claimants, as though every Friday he sits down with his card reader to do some online banking, sneaking into people’s accounts and spiriting their cash away to the scrounging masses. Anyone who has come within ten feet of claiming benefits knows it is far from a simple process.
He is incredulous that if a doctor says you are too sick to work, you get signed off work, as though doctors are untrained apes that somehow gained access to a pen. This is only the latest absurd episode in DWP’s ongoing deep mistrust of the medical profession, whose knowledge of their own patients is often ignored in favour of a brief assessment by an outside agency. IDS implies it is yes-no question that GPs ask; you’re either well enough to work or signed off indefinitely to leech from the state. This is simply not true. GPs can recommend their patients for differing approaches for remaining in work, be it a phased return or adapted circumstances and they do tend to have the advantage over the DWP’s agency of having actually met their patient before.
I have read enough stories of the callous ineptitude of sanctions and cuts starving the people we are meant to be protecting. A robust welfare system is the sign of a society that cares for those in need. We need to provide accessible, suitable jobs for those who can work and accessible, suitable benefits for those who can’t. That truly would be a gift that keeps giving.