Investigating the Phillips Curve's Instability in Iran's Economy Using the State-Space Approach

Philips curve studies are one of the major issues of macroeconomics and have long been tested in empirical studies. Hybrid New Keynesian Phillips Curve developed by Galí and Gertler, generally believes that in the short-run there is a trade-off between inflation and excess demand due to nominal rigidities, while inflation in the long run is constant at the Non-Accelerating Inflation Rate of Unemployment (NAIRU). By contrast, Gordon in his triangle model assumes the NAIRU to be variable over time. In this regard, the present study, using by Time-Varying Parameter approach tries to create a new insight into the validity of the Philips curve in the Iran's economy. In this way, the data for the period 1960-2016 have been used. Given the conditions of the Iran's economy, the coefficients were estimated at six time points. The results show that the Phillips curve parameters in the Iran's economy are not stable. So that the share of forward-looking expectations in this instability is significant. The coefficients obtained for the output gap showed that in the most years the slope of the Philips curve in the Iran's economy has been positive, and its validity cannot be generally confirmed. Accordingly, it is impossible to make a definite statement about the Phillips curve subordinate form.