How should one measure the natural rate of unemployment? This paper proposes a systems procedure as an alternative to NAIRU. The natural rate is treated as an unobserved state variable in a system that includes measurement equations for the unemployment rate, the rate of wage growth and the rate of inflation. The model is derived from a version of the wage bargaining model of Blanchard and embodies a version of the natural rate hypothesis. The model is estimated by embedding the Kalman filter within the full-information maximum likelihood procedure. For US data, the estimated model implies substantial post-war variation in the natural rate and a negative, but weak, effect of inflation surprises on unemployment.
