The work of winner of 2011's economics Nobel prize, Christopher Sims is empirical and, therefore, directly useful to policymakers. He  has used a powerful but relatively simple analytical tool, called vector autoregression, to explain why different things like income and inflation take different periods of time to respond to a change in, say, interest rates. 

His work establishes that the effect of a rate hike on the GDP is immediate and causes a contraction; inflation takes longer to respond and starts cooling only after five or six quarters. The research has been so influential that most central banks worldwide structure their policies with his results built into them. 

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