Does tracking price momentum across spending categories improve inflation forecasts?
Core argument: The Inflation Shock Momentum Index improves PCE inflation forecasts at 1–3 year horizons beyond standard predictors, signaling emerging price pressures.
This Economic Letter describes a new indicator called the Inflation Shock Momentum Index (ISM), which provides a timely signal of emerging inflationary or disinflationary pressures. We construct the ISMI by sorting categories of the personal consumption expenditures (PCE) basket of goods and services into groups based on the pattern of recent monthly surprises, called inflation shocks. Positive momentum categories are identified as those with three consecutive positive inflation shocks, while negative momentum categories are identified as those with three consecutive negative inflation shocks. The ISMI represents the expenditure-weighted share of inflation categories with positive momentum minus the share with negative momentum.The ISMI helps improve forecasts of overall PCE inflation at horizons of one to three years, even after accounting for standard predictor variables. Panel A of Figure 1 plots the ISMI together with 12-month PCE inflation. Pronounced positive or negative fluctuations of the index align well with historical inflation narratives.

