In the United States, the Federal Reserve has a dual mandate of promoting stable inflation and maximum employment. Since the Fed directly controls only one instrument—the federal funds rate—the authors argue that the Fed's priorities continuously alternate between inflation and economic activity. In this paper, the authors assume that the effective weights put by the Fed on different indicators vary over time. To test this assumption, they estimate a monetary policy priority index by adding non-linear endogenous weights to a conventional Taylor-type rule.

In a departure from the existing literature, the authors do not try to distinguish between longlasting monetary policy regimes. Instead, their model allows the Fed's priorities to vary continuously. It is therefore possible to assess the Fed's priorities at any given time during the Greenspan era. Further, the authors' non-linear reaction function specification allows the Fed to react more agressively to inflation the more expected inflation diverges from an implicit target. The specification takes into account the accepted idea that the Fed's inflation mandate ultimately prevails over its economic activity mandate.

The authors' results are intuitive and corroborated by historical evidence. Indeed, the monetary policy indexes show that the Fed's focus was mainly on inflation over the first 10 years of Greenspan's term as Fed chairman. Then, around 1998, economic activity became the Fed's main focus. This is consistent with the gain in the Fed's credibility over the Greenspan era.