Revisionist history: how data revisions distort economic policy research

This article describes how and why official U.S. estimates of the growth in real economic output and inflation are revised over time, demonstrates how big those revisions tend to be, and evaluates whether the revisions matter for researchers trying to understand the economy’s performance and the contemporaneous reactions of policymakers. The conclusion may seem obvious, but it is a point ignored by most researchers: To have a good chance of understanding how policymakers make their decisions, researchers must use not the final data available, but the data available initially, when the policy decisions are actually made.