US economists Alvin Roth and Lloyd Shapley have won the 2012 economics Nobel prize.

The pair were awarded the prize for research on how to match different economic agents, such as students for schools or even organ donors with patients.

The Royal Swedish Academy of Sciences, which made the award, said the 8 million crown (€920,000) prize recognised "the theory of stable allocations and the practice of market design".

The economics prize, officially called the Sveriges Riksbank Prize in Economic Sciences in Memory of Alfred Nobel, was established in 1968.

It was not part of the original group of awards set out in Nobel's 1895 will.

Life-saving kidney exchange programmes are just one of the practical applications of the market-matching theories the pair devised.

Tore Ellingsen, a Nobel committee member and a professor at the Stockholm School of Economics, said the central question when resources are scarce is who gets what.

"Which worker gets which job? Which student gets to go to which school? Which patient gets access to which transplantable organ. Matching theory explains how outcomes depend on the chosen matching procedure," Prof Ellingsen said.

The award citation said Prof Shapley, an emeritus professor at the University of California Los Angeles, had used game theory to compare various matching methods and make sure the matches were acceptable to all counterparts.

Prof Roth followed up on Prof Shapley's results in a series of empirical studies.

"I am sure when I go to class this morning, my students will pay more attention," Prof Roth, who teaches at Stanford and Harvard, told a news conference by telephone from California.

Prof Roth, who was sleeping when the call from Stockholm came and missed the first call, said the award was unimaginable and unexpected: "It certainly is expected that Lloyd Shapley should win the prize. It would have been a grave oversight if he did not. So I am glad to share it with him."

He said: "Matching ... is about how you get all the things that you can't just choose but you also have to be chosen - so getting into university, getting married, getting jobs," he told Reuters.

"You can't just have what you want; you also have to do some courtship and there is courtship on both sides and we study the market place processes by which those types of courtship are resolved."

Prof Roth is a co-founder of the New England Program for Kidney Exchange,, which draws on the theory of matching markets to bring together pairs of compatible kidney donors and recipients.

"This is very much what economics is about," said Prof Ellingsen, the Swedish professor.

"How to allocate scarce resources as well as possible, to economise."