The Intermittent Phillips Curve: Finding a Stable (But Persistence-Dependent) Phillips Curve Model Specification

We establish that the Phillips curve is persistence-dependent: inflation responds differently to persistent versus moderately persistent (or versus transient) fluctuations in the unemployment rate gap. This persistence-dependent relationship appears to align with business-cycle stages and is thus consistent with existing theory. Previous work fails to model this dependence, thereby finding numerous "inflation puzzles" – e.g., missing inflation/disinflation – noted in the literature. Our specification eliminates these puzzles; for example, the Phillips curve has not weakened, nor was inflation "stubbornly low" in 2019. The model's coefficients are stable, and it provides accurate conditional recursive forecasts through the Great Recession. There are important monetary policy implications.