Estimation of Fiscal Reaction Functions and Determinants of Fiscal Sustainability in Iran Employing Linear and Nonlinear Functions

Governments pursue macroeconomic objectives such as stabilizing the economy by employing fiscal policy tools. However, fiscal sustainability is obligatory for achieving economic stability. This research, utilizing linear and nonlinear fiscal reaction functions, including quadratic and cubic, time-varying parameter and Markov-switching fiscal regime change functions, measures the fiscal sustainability of the Iranian government and its determinants in the period 1970-2021. Based on the findings of this research, the government debt-to-GDP ratio in linear and nonlinear models is negative and insignificant, but in the model with control variables, it is negative and strongly significant. Hence, the model with control variables results in the unsustainability of Iran's fiscal policy. The results of Markov-switching fiscal regime change model reveals the existence of two fiscal regimes in Iran's fiscal policy. An unsustainable fiscal regime, in which the reaction of the primary budget balance to the public debt is negative and significant, and a sustainable fiscal regime in which the reaction of the primary budget balance to the public debt is positive but insignificant. Also, the results of the Markov-switching fiscal regime change model demonstrates that the average filtered and smoothed transmission probabilities of remaining in unsustainable fiscal regime is higher than that of sustainable fiscal regime, which indicates that Iran's fiscal policy has been unsustainable. Based on the results of the time-varying parameter model, the reaction of the primary budget balance to the debt expansion has been negative and diminishing, therefore, debt reduction has not been the priority of governments in Iran, and as a result, Iran's fiscal policy has been proceeding in the unsustainable direction.