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.

Show Hide image

Overlooking the effect of Brexit on Northern Ireland is dangerous for the whole UK

We voted to remain in the European Union. The tensions caused by the referendum outcome, and ignoring its effect on us, will cause utter carnage in Northern Ireland.

I’ve been from Northern Ireland all my life. Having spent many years living in Dublin, and now London, I’m quite used to that very fact making people uncomfortable. I get it. From a glance at the news, it would seem we fight each other about flags and anthems and are inexcusably proud of throwing glass at people in bowler hats, or daubing on our own homes the worst paintings ever committed to brickwork. Our tiny little protectorate has generated such disproportionate levels of confusing violence, most people are terrified of saying the wrong thing about any of it. We’re the celiac vegans of nationalities; the worry is that almost anything you offer will offend.

Most people avoid such worries by – whisper it – simply never acknowledging that we exist. This reflexive forgetfulness is, of course, a happy state of affairs compared to what went before. I refer, of course, to the period named, with that Ulster-tinged strain of sardonic understatement, the Troubles, when some 3,600 people were killed and ten times that injured. By some estimates, as many as 115,000 people lost a close relative to violence in this time, and many more a good friend, a colleague or an old school pal. Taken as a portion of 1.5m people, this means a startlingly high percentage of Northern Irish citizens have been directly affected by the conflict, certainly a higher percentage than that of, say, the English electorate who have ever voted for Ukip.

Northern Ireland also contains Britain’s only fully open border with the EU. I know because I grew up on it, specifically between Derry and Donegal, where my dad's back fence demarked an invisible boundary, a small hop from the UK to the Republic, and back. From a migration point of view, this poses a problem, so when Brexit was being deliberated, it did seem odd that Northern Ireland was barely mentioned at all, that the one border that exists in the entire country was given such scant reference during the campaign’s interminable duration. A dreaded EU migrant, travelling freely through Ireland toward my father’s house will not be subject to border checks once he has passed it quietly behind him. No machine guns, no "papers please", none of the fortified rigour mandated by the Leave campaign. Implementing such fortifications would, of course, be a practical nightmare, since so many live in Ireland but work in the UK, and vice versa. But the psychological effect of such a move would be infinitely worse.

Much of the Good Friday Agreement was predicated on free movement between north and south, and cross-border bodies that reinforced a soft-union of the two states; just enough to ameliorate nationalists, but nothing so resembling a united Ireland as to antagonise unionists. Making Irish-identifying Northern Irish citizens undergo any form of border checkpoint between the two countries would not just be a bureaucratic hassle, it would massively inhibit the self-determination nearly half of Northern Ireland's population takes from both countries’ status within a wider European state.

The peace that exists rests largely on this status quo, the acceptance of people who reject violent means and see little injustice in being allowed to live their lives within a British state that dignifies their close connection to their southern neighbours. It is hard to overstate how different this situation would be were armed checkpoints to re-emerge. I remember checkpoints as a child. I remember machine guns and dogs and my dad making sure we weren't nervous while he was being interrogated by armed men inspecting his driving license and checking under our car for explosives. This was every day. Rather than some novel development, this will be a direct, unbidden return to something we worked very, very hard to get away from, something we were promised was over, and something for which thousands of very stubborn, dangerous people struck what many considered a highly improbable truce.

It is this effort to which thousands of Northern Irish people now owe their lives, to which tens, perhaps hundreds, of thousands more can count among the living and healthy their siblings, their friends, their colleagues. This may not be at the forefront of minds in Carlisle or Cornwall or aboard the statesmanlike grandeur of a battlebus, but it is the lived reality of Northern Irish people. To stoke up these tensions risks sleepwalking out of a peace that was hard-fought and long considered unthinkable. To do so as a side effect of what appears to be, on its face, little more than a tussle for the leadership of a single political party with little-to-no presence in Northern Ireland seems distasteful in the extreme.

Having stating these facts to friends here in London, I’ve been touched by their sorrow for our plight but, for all their sympathy, it might still not have registered that our problems have a tradition of travelling to people in London and Dublin, in Birmingham and in Monaghan. If greater care is not given to the thoughts, aspirations and fears of Northern Irish people, and those still-present agents of chaos who would seek to use such discontent to their own violent ends, we risk losing a lot more than free use of bagpipes or pleasingly bendy bananas.

Westminster must listen to those who would bear the burden of Fortress Britain’s turrets near their homes or else, to borrow a phrase, Brexit will be a threat to our national security, our economic security and your family's security.

Séamas O'Reilly is a writer and musician. He tweets @shockproofbeats. His website is