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.

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Forget the progressive alliance - it was the voters wot won it in Richmond

The Labour candidate on how voters have acted tactically for decades.

The Richmond Park by-election is both a triumph and a setback for the concept of an anti-Tory progressive alliance. As the Labour candidate, I was bombarded with emails and tweets saying I ought to stand down to prevent Zac Goldsmith being re-elected long after it was technically impossible for me to do so even if I had wanted to. I was harangued at a meeting organised by Compass, at which I found myself the lonely voice defending Labour's decision to put up a candidate.

I was slightly taken aback by the anger of some of those proposing the idea, but I did not stand for office expecting an easy ride. I told the meeting that while I liked the concept of a progressive alliance, I did not think that should mean standing down in favour of a completely unknown and inexperienced Lib Dem candidate, who had been selected without any reference to other parties. 

The Greens, relative newbies to the political scene, had less to lose than Labour, which still wants to be a national political party. Consequently, they told people to support the Lib Dems. This all passed off smoothly for a while, but when Caroline Lucas, the co-leader of the Greens came to Richmond to actively support the Lib Dems, it was more than some of her local party members could stomach. 

They wrote to the Guardian expressing support for my campaign, pointing out that I had a far better, long-established reputation as an environmentalist than the Lib Dem candidate. While clearly that ultimately did little to boost my vote, this episode highlighted one of the key problems about creating a progressive alliance. Keeping the various wings of the Labour party together, especially given the undisciplined approach of the leader who, as a backbencher, voted 428 times during the 13 years of Labour government in the 1990s and 2000s, is hard enough. Then consider trying to unite the left of the Greens with the right of the Lib Dems. That is not to include various others in this rainbow coalition such as nationalists and ultra-left groups. Herding cats seems easy by contrast.

In the end, however, the irony was that the people decided all by themselves. They left Labour in droves to vote out Goldsmith and express their opposition to Brexit. It was very noticeable in the last few days on the doorstep that the Lib Dems' relentless campaign was paying dividends. All credit to them for playing a good hand well. But it will not be easy for them to repeat this trick in other constituencies. 

The Lib Dems, therefore, did not need the progressive alliance. Labour supporters in Richmond have been voting tactically for decades. I lost count of the number of people who said to me that their instincts and values were to support Labour, but "around here it is a wasted vote". The most revealing statistic is that in the mayoral campaign, Sadiq Khan received 24 per cent of first preferences while Caroline Pidgeon, the Lib Dem candidate got just 7 per cent. If one discounts the fact that Khan was higher profile and had some personal support, this does still suggest that Labour’s real support in the area is around 20 per cent, enough to give the party second place in a good year and certainly to get some councillors elected.

There is also a complicating factor in the election process. I campaigned strongly on opposing Brexit and attacked Goldsmith over his support for welfare cuts, the bedroom tax and his outrageous mayoral campaign. By raising those issues, I helped undermine his support. If I had not stood for election, then perhaps a few voters may have kept on supporting him. One of my concerns about the idea of a progressive alliance is that it involves treating voters with disdain. The implication is that they are not clever enough to make up their mind or to understand the restrictions of the first past the post system. They are given less choice and less information, in a way that seems patronising, and smacks of the worst aspects of old-fashioned Fabianism.

Supporters of the progressive alliance will, therefore, have to overcome all these objections - in addition to practical ones such as negotiating the agreement of all the parties - before being able to implement the concept. 

Christian Wolmar is an award winning writer and broadcaster specialising in transport. He was shortlisted as a Labour mayoral candidate in the 2016 London election, and stood as Labour's candidate in the Richmond Park by-election in December 2016.