Real Business Cycle Theory: Wisdom or Whimsy?

This paper assesses the empirical plausibility of the view that aggregate productivity shocks account for most of the variability in post World War II US output. We argue that the type of evidence forwarded by proponents of this proposition is too fragile to be believable. First, our confidence in the evidence is fundamentally affected once we abandon the fiction that we actually know the true values of the structural parameters of standard Real Business Cycle (RBC) models. What the data are telling us is that, while productivity shocks play some role in generating the business cycle, there is simply an enormous amount of uncertainty about just what percent of aggregate fluctuations they actually do account for. The answer could be 70% as Kydland and Prescott (1989) claim, but the data contain almost no evidence against either the view that the answer is really 5% or that the answer is really 200%. Second, we show that point estimates of the importance of technology shocks are extremely sensitive to small perturbations in the theory. Allowing for labor hoarding behavior in an otherwise standard RBC model reduces the ability of technology shocks to account for aggregate fluctuations by 50%. This finding provides some support for the view that many of the movements in the Solow residual which are labelled as productivity shocks may be an artifact of labor hoarding type phenomena.