The Phillips curve keeps changing sign
This chart shows how the estimated relationship between inflation and unemployment changes across rolling 20-year windows. The repeated sign changes demonstrate instability in the simple bivariate relationship rather than a stable policy rule.
What does it show?
The 20-year inflation–unemployment slope was negative in only 46% of the available windows—and repeatedly flipped sign.
Methodology
For every complete rolling 20-year window, regresses annual-average CPI inflation on annual-average U-3 unemployment and plots the unemployment coefficient. The exercise shows how unstable the unconditional bivariate relationship is; it does not control for expectations, supply shocks, monetary policy, lags, or changes in inflation dynamics.