The NAIRU is 3.9%
The constant term in the Phillips curve specification no longer makes sense when there is a vacancy term included to offset the unemployment term. (See the comments section of my previous post on the subject.) My new specification, and a slight correction to the April 2006 data point, results in a NAIRU of 3.9%. The chart below (click on image for a better picture) shows what has happened to it over time, based on a single Phillips curve fit and a constant-slope Beveridge curve which shifts continuously. The results are surprisingly consistent with actual monetary policy (except over the past year, but lately energy price concerns might outweigh NAIRU concerns).