Overview

The Phillips curve describes an observed inverse relationship between unemployment and inflation in an economy: when unemployment is low, inflation tends to be higher, and when unemployment is high, inflation tends to be lower. The original formulation focused on wage inflation rather than price inflation and suggested a stable trade-off that policymakers might exploit. The basic idea is that tighter labor markets push up wages, which then feed into broader price increases.

Original finding and empirical pattern

The concept traces to the empirical study by A. W. Phillips, who examined decades of British data and reported a clear negative correlation between the unemployment rate and the rate of change in money wages. His work prompted economists to plot a curve summarizing the relationship between unemployment and inflation and spurred follow-up research in other countries. Early interpretations treated the curve as a useful descriptive tool for short-run fluctuations in economic activity.

Theoretical developments and expectations

In the 1960s and early 1970s economists such as Milton Friedman and Edmund Phelps argued that expectations about future inflation alter the trade-off. If workers and firms expect higher inflation, wage demands and price-setting adjust accordingly, shifting the short-run curve. Friedman introduced the idea of a natural rate of unemployment and predicted a vertical long-run Phillips curve: in the long run, inflation cannot permanently lower unemployment. This view linked the observed trade-off to temporary deviations from the natural rate rather than a lasting policy menu.

1970s stagflation and revisions

During the 1970s many economies experienced stagflation — simultaneous high inflation and high unemployment — which undermined the simple inverse relationship and highlighted the role of supply shocks (for example, oil price shocks) and changing inflation expectations. Economists refined the framework to include adaptive and rational expectations and to emphasize that supply-side disturbances and credibility of monetary policy matter. These refinements explained why the trade-off can disappear or invert under certain conditions.

Uses, limitations, and policy implications

Central banks still consider Phillips-curve concepts when assessing inflationary pressures and labor market slack, though modern policy analysis treats the relationship as conditional and shifting rather than fixed. The curve can help illustrate short-run trade-offs, inform inflation forecasts, and guide communication about expected policy actions. Critics point out that empirical estimates vary over time and across countries, that measurement issues (such as the natural rate or NAIRU) are uncertain, and that supply shocks can dominate the dynamics.

Key concepts and notable facts

  • Wage vs. price inflation: Phillips originally studied wage inflation; many modern variants focus on consumer price inflation (CPI).
  • Short run vs. long run: The short-run curve may slope downward; the long run is often modeled as vertical at the natural rate (natural unemployment).
  • Expectations: Adaptive and rational expectations change where the curve lies (expectations).
  • Stagflation: The 1970s experience showed the simple trade-off could break down (stagflation).
  • Policy use: Monetary policy aims to balance inflation and employment objectives, mindful of credibility and lags (policy).

For further empirical studies, theoretical treatments, and modern applications in central banking, see specialized literature and institutional analyses (empirical work, theory surveys, policy reports).