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
Show Hide image

George Osborne's mistakes are coming back to haunt him

George Osborne's next budget may be a zombie one, warns Chris Leslie.

Spending Reviews are supposed to set a strategic, stable course for at least a three year period. But just three months since the Chancellor claimed he no longer needed to cut as far or as fast this Parliament, his over-optimistic reliance on bullish forecasts looks misplaced.

There is a real risk that the Budget on March 16 will be a ‘zombie’ Budget, with the spectre of cuts everyone thought had been avoided rearing their ugly head again, unwelcome for both the public and for the Chancellor’s own ambitions.

In November George Osborne relied heavily on a surprise £27billion windfall from statistical reclassifications and forecasting optimism to bury expected police cuts and politically disastrous cuts to tax credits. We were assured these issues had been laid to rest.

But the Chancellor’s swagger may have been premature. Those higher income tax receipts he was banking on? It turns out wage growth may not be so buoyant, according to last week’s Bank of England Inflation Report. The Institute for Fiscal Studies suggest the outlook for earnings growth will be revised down taking £5billion from revenues.

Improved capital gains tax receipts? Falling equity markets and sluggish housing sales may depress CGT and stamp duties. And the oil price shock could hit revenues from North Sea production.

Back in November, the OBR revised up revenues by an astonishing £50billion+ over this Parliament. This now looks a little over-optimistic.

But never let it be said that George Osborne misses an opportunity to scramble out of political danger. He immediately cashed in those higher projected receipts, but in doing so he’s landed himself with very little wriggle room for the forthcoming Budget.

Borrowing is just not falling as fast as forecast. The £78billion deficit should have been cut by £20billion by now but it’s down by just £11billion. So what? Well this is a Chancellor who has given a cast iron guarantee to deliver a surplus by 2019-20. So he cannot afford to turn a blind eye.

All this points towards a Chancellor forced to revisit cuts he thought he wouldn’t need to make. A zombie Budget where unpopular reductions to public services are still very much alive, even though they were supposed to be history. More aggressive cuts, stealthy tax rises, pension changes designed to benefit the Treasury more than the public – all of these are on the cards. 

Is this the Chancellor’s misfortune or was he chancing his luck? As the IFS pointed out at the time, there was only really a 50/50 chance these revenue windfalls were built on solid ground. With growth and productivity still lagging, gloomier market expectations, exports sluggish and both construction and manufacturing barely contributing to additional expansion, it looks as though the Chancellor was just too optimistic, or perhaps too desperate for a short-term political solution. It wouldn’t be the first time that George Osborne has prioritised his own political interests.

There’s no short cut here. Productivity-enhancing public services and infrastructure could and should have been front and centre in that Spending Review. Rebalancing the economy should also have been a feature of new policy in that Autumn Statement, but instead the Chancellor banked on forecast revisions and growth too reliant on the service sector alone. Infrastructure decisions are delayed for short-term politicking. Uncertainty about our EU membership holds back business investment. And while we ought to have a consensus about eradicating the deficit, the excessive rigidity of the Chancellor’s fiscal charter bears down on much-needed capital investment.

So for those who thought that extreme cuts to services, a harsh approach to in-work benefits or punitive tax rises might be a thing of the past, beware the Chancellor whose hubris may force him to revive them after all. 

Chris Leslie is chair of Labour's backbench Treasury committee.