New Study Unveils “Main Monetary Policy” Shock to Sharpen Measurement of Central Bank Surprises

Economists have long tried to isolate “monetary policy shocks”—unexpected moves in policy that ripple through the economy—in order to measure how central bank decisions drive the business cycle. In a new study, Christoph Boehm, Husang Kim, and T. Niklas Kroner introduce a method they say can extract a single dominant disturbance from the many market-based measures of monetary surprises used in the literature.

Their approach defines what they call a “main monetary policy” (MMP) shock: the particular linear combination of observed monetary policy surprises that best accounts for movements in key macroeconomic variables. Rather than choosing one surprise series—say, a change in short-term interest rate futures around Federal Reserve announcements—the procedure searches across surprises and weights them to maximize explanatory power for broader economic fluctuations.

To implement the idea, the authors combine three inputs that are standard or emerging in empirical monetary economics. Two are conventional high-frequency yield-curve surprises derived from market moves around policy announcements. The third is the “non-yield” shock developed in Boehm and Kroner (2024), intended to capture policy-relevant news that is not well summarized by shifts in interest rates along the yield curve.

Using this set of surprises, the authors report that the resulting MMP shock explains meaningful variation in U.S. business-cycle dynamics over roughly the past three decades. That conclusion stands out because earlier work often found that standard measures of monetary policy surprises account for only a limited share of macroeconomic fluctuations once other forces are considered.

The character of the identified shock is also notable. In textbook accounts, a contractionary monetary policy shock pushes interest rates up, tightens financial conditions, slows output, and eventually reduces inflation. By contrast, the study’s contractionary MMP shock leaves interest rates “mostly unchanged” on impact. Even so, it is associated with a sustained decline in headline prices and a strengthening of the U.S. dollar. The authors also find that financial conditions tighten for a time and industrial production falls, indicating real economic restraint despite the muted interest-rate response.

The paper situates these findings within the ongoing debate about what high-frequency market moves around central bank communications actually measure—pure policy actions, information revealed about the economy, or broader changes in risk sentiment and expected inflation. The MMP framework, the authors argue, provides a systematic way to distill the portion of monetary surprises that matters most for macroeconomic outcomes.

The authors thank a number of economists for feedback, including Olivier Coibion, Thomas Drechsel, Lutz Kilian, Karel Mertens, Emi Nakamura, Alexander Richter, Jon Steinsson, and seminar participants at the Federal Reserve Bank of Dallas. They also credit Hyungjin Kim for research assistance. The study notes that the views expressed are those of the authors and not necessarily those of the Federal Reserve Board, the Federal Reserve System, the University of Texas at Austin, or the National Bureau of Economic Research.

Why it matters

If monetary policy shocks can restrain the economy and lower prices without visibly moving interest rates, standard narratives—and some empirical tools—may be missing the channel that matters most. Investors, forecasters, and policymakers could need broader measures of policy “surprises” beyond yields to understand how Fed communications and actions transmit to inflation, the dollar, and production. What to watch next is whether this MMP shock remains robust with alternative data and whether it can improve real-time assessments of policy stance.