Evening Must-Read: Roger Farmer: Real Business Cycle Theory and the High School Olympics

Roger Farmer:
Real business cycle theory and the high school Olympics:
“I have lost count of the number of times…

…I have heard students and faculty repeat the idea in seminars, that ‘all models are wrong’. This aphorism, attributed to George Box, is the battle cry  of the Minnesota calibrator, a breed of macroeconomist, inspired by Ed Prescott…. The cry has been used for three decades to poke fun at attempts to use serious econometric methods to analyze time series data. Time series methods were inconvenient to the nascent Real Business Cycle Program that Ed pioneered because the models that he favored were, and still are, overwhelmingly rejected by the facts. That is inconvenient.

Ed’s response was pure genius. If the model and the data are in conflict, the data must be wrong…. In a puff of calibrator’s smoke, the history of time series econometrics was relegated to the dustbin of history to take its place alongside alchemy, the ether, and the theory of phlogiston. How did Ed achieve this remarkable feat of prestidigitation? First, he argued that we should focus on a small subset of the properties of the data….

Ed argued that the trends in time series are a nuisance if we are interested in understanding business cycles and he proposed to remove them with a filter… remov[ing] a different trend from each series and the trends are discarded when evaluating the success of the theory…. He proposed that we should evaluate our economic theories of business cycles by how well they explain co-movements among the wiggles.

When his theory failed to clear the 8ft hurdle of the Olympic high jump, he lowered the bar to 5ft and persuaded us all that leaping over this high school bar was a success. Keynesians protested. But they did not protest loudly enough and ultimately it became common, even among serious econometricians, to filter their data with the eponymous Hodrick-Prescott filter….

We don’t have to play by Ed’s rules…. Once we allow aggregate demand to influence permanently the unemployment rate, the data do not look kindly on either real business cycle models or on the new-Keynesian approach. It’s time to get serious about macroeconomic science and put back the Olympic bar.