Two US academics have won the 2011 Nobel economics prize.
The Royal Swedish Academy of Sciences cited ''empirical research'' by Thomas Sargent and Christopher Sims ''on cause and effect in the macroeconomy''.
They studied how economic policy, such as raising interest rates or cutting taxes, affects macroeconomic variables such as GDP and inflation.
Sargent, 68, is a professor of economics at New York University. Sims, also 68, is a professor of economics and banking at Princeton University.
The award - official name, the Sveriges Riksbank Prize in Economic Sciences in Memory of Alfred Nobel - was not part of the original group of awards set out in Nobel's 1895 will, but was established by Sweden's central bank, the Riksbank, in 1968.
The five main prizes are in physics, chemistry, medicine, literature and peace.