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The purpose of this paper is estimating output gap as one of the variables that affect inflation in the Iranian economy. Therefore, using seasonal data from spring 1989 to winter 2006 and through Hodrick-Prescott filtering techniques the potential output and output gap are estimated and then ordinary least squares approach has been used to find out the relationship between inflation and output gap. Variables such as exchange rates, price index of imported goods, and the adjusted output gap as real variables and expected future inflation have been used for estimating the model considering the facts and theories in the Iranian economy. This test has been done through the rational expectation hypothesis of an enterprise and using a new Keynesian Phillips curve. The research findings verify the new Keynesian opinion. Thus, in Iran where the average rate of inflation in the period, is 19.6% and therefore considered among the countries with galloping rate of inflation, Phillips curve has been estimated with a relatively steep slope. In the long run, the steep Phillips curve according to Keynesians implies that in case of demand shock, the production will increase and compared with the new classic models it has less impact on inflation.

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This paper tests monetary view of inflation in Iranian economy by a monetary approach within P* model using OLS and ARDL techniques during 1358-1387 (1979-2008). It should be noted that only the standard P* model (domestic price gap) is tested in this study. Regarding that domestic price gap consists of output and velocity gaps, the Hedrick – Prescott filter method is used to estimate the potential production level and the velocity of balanced money. Estimation results of various models show that the standard P* model (domestic price gap), is not able to explain and forecast inflation in Iranian economy and implies that the quantity theory of money is not correct in Iranian economy. Therefore, we investigated monetary theory of inflation using alternative variables including volume of liquidity, real gross domestic product (GDP), informal exchange rate, import price index with using ARDL method. Results show that a 10% growth of liquidity leads to increase general prices by 4.6%. Thus, the monetary hypothesis of inflation is partially confirmed, however concerning that relationship between inflation and liquidity volume is not unique, and other factors affect inflation in Iran, therefore to curb Iranian inflation we cannot adopt only monetary policy as an effective tool.

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Inflation is the main problem which should be overcome both by the government and economic agents. The existence of inflation in an economy causes distortion and disequilibrium in the macroeconomic variables in the forms of decreasing growth rate, rising unemployment rate and uneven income distribution and so on. In addition, the uncertainties caused by the high inflation rates, raise the inflation expectations. This paper tries to found out which type of inflation expectations gives the better explanation of current inflation: backward-looking, forward-looking or some combination of the two? Using Generalized Method of Moments (GMM) and annual data over the period 1976-2008, the results of hybrid Philips model  show that inflation in Iran is significantly determined by backward-looking inflation expectations, forward-looking inflation expectations, the output gap, exchange rate, and liquidity growth. However, backward-looking inflation expectations are more important than forward-looking expectations. The findings imply that managing inflation expectations, liquidity growth, and exchange rate can complement each other to achieve overall price stability.

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One of the most important issues in monetary and fiscal policy analysis is their efficiency or effectiveness, which tells policymakers about effectiveness of policies. In general, the effectiveness or effectiveness of monetary and fiscal policies refers to the extent to which they affect equilibrium national output or income.  Therefore, in order to achieve its goals, the policymaker should be able to respond appropriately to the production gap and inflation accordingly, a policy rule covering the goals of the central bank should be used. In this study, in the framework of Taylor rule, the response of monetary and fiscal policies to the output gap has been investigated in the Iranian economy using the Quantile regression method over the period 1976-2018. The results show that by increasing the output gap in different quantities, monetary authorities do not show any reaction to the output gap. But government policymakers pursue an expansionary policy toward the output gap, which is contrary to Taylor's rule, and the results confirm that government policymakers make policy at their will.