This study examines the nonlinear impact of urbanization on public sector expenditure in Iran during the years of 1960-2014. For this purpose, is used the Smooth Transition Regression model (STR) as one of the most prominent regime-switching models. The estimated STR model supports a nonlinear threshold behavior in the relationship between urbanization and public sector expenditure in the country in a two regime structures with a threshold (optimum) level of about 55. 28%. In the first regime, urbanization has a negative impact on public sector expenditure, because of positive external consequences and economies of scale in the production of public goods, but after crossing the threshold level (the amount of 55. 28 percent), in second regime, its impact is positive, due to occurrence of the phenomenon external crowded and some negative external consequences. Accordingly, it can be said that the hypothesis of U-shaped impact of the urbanization on public sector expenditure has been confirmed in the Iran.

Regarding the important role of health in economic growth and development, the purpose of the present paper is to investigate the impact of life expectancy, as the most important indicator of health, on economic growth in Iran during 1965-2009. The estimated Smooth Transition Regression (STR) model supports a nonlinear threshold behavior in the relationship between life expectancy and economic growth in the country in a two regime structures with a threshold level of 55.34 years. In other words, our findings are both consistent with Acemoglu and Johnson (2007) for the negative impact and with demographic transition theory for the reducing effect of life expectancy on economic growth in Iran. This shows the country is approaching the stage of the fertility transition, where the increase in life expectancy will bring about a decline in population.

Objective: This study is trying to analyze the behavior of monetary policymakers with using Taylor's rule. Policy rules express how monetary policy tools respond to changes in state variables. In recent decades, has been one of the main and mental preoccupations of monetary economists  hat how monetary policymakers react to key economic variables and has led to more studies on the formulation and evaluation of monetary policy rules.Method: Since it is not expected to have a linear relationship between the variables of the model due to the existence of successive structural changes and changes in the political regime, therefore, the smooth transition threshold regression model (STR) has been used for respect to the variables of oil price changes, official exchange rate changes, inflation gap and production gap in the annual period from 2002 to 2019. It should be noted that the variables used in estimating the models are based on the degree of stationarity of the variables. According to the econometric literature, before any estimation, in order to prevent the occurrence of false regressions, it is necessary to ensure that the variables are stationary. For this purpose, the generalized Dickey-Fuller unit root test (ADF) has been used. The results obtained in table (1) show that in all the studied countries, the production gap variables, official exchange rate changes, inflation gap, oil price changes and nominal interest rate changes (for Iran; real interest rate changes) in The surface is static. In the next step, to estimate an STR model, it is necessary to determine the optimal interval for the model variables. After determining the optimal interval for the research variables, the type of model is determined in terms of linearity or non-linearity. For this purpose, the F test statistic was used. In the following, the appropriate transfer variable should be selected for the nonlinear model. To select the transition variable, any potential explanatory variable can be tested, but priority is given to the transition variable that rejects the null hypothesis of the f-test more strongly. Before estimation, model parameters using Newton-Raphsen algorithm are first checked for the existence or non-existence of collinearity between the variables of the model using the collinearity test of the variance inflation factor (Vif). In the following, the mentioned models are estimated and an attempt is made to analyze the models in which the variables have the greatest impact on the monetary policy maker and Taylor's principle is observed in them.Results: The results showed that, firstly, the reaction function of monetary policy makers in 16 selected countries is non-linear. Secondly; The findings from the estimation of the specified policy rule based on models (1), (2), (3) and (4) have shown that in all the investigated countries, by entering the variables of oil price changes and the official exchange rate into Taylor's model (model 1), the targeting of monetary policy makers is stable. Meanwhile, for the country of Iran, with the inclusion of the variables of oil price changes and official exchange rate in the Taylor model, inflation targeting is changed to production targeting. Thirdly; Based on the results obtained from the estimation of models, it can be seen that the variable of oil price changes in the countries of Algeria, Qatar, Kazakhstan, Ecuador, Colombia, Malaysia, Mexico, Belarus and Bulgaria affects the reaction function of monetary policy makers through the production gap channel and in Iran, Russia, Angola, Nigeria, Brazil, Tunisia and Azerbaijan through the official exchange rate gap channel.Conclusion: It is suggested that the central banks of the countries use key and influential variables such as: changes in oil prices, stock prices, housing prices, exchange rates, etc., because the selection of inappropriate policy goals damages the credibility of the central bank and invalidates the targeting framework.

The reaction function of the monetary policy maker can provide insight into the factors influencing monetary policy decisions. Empirical estimates indicate the existence of differences among countries, whether monetary policy only reacts to expected inflation or takes into account expected production developments. This study investigates the reaction function of the Iranin central bank, focusing on the variation in nominal interest rate as the main instrument for monetary policy. For this purpose, we analyzed  the reaction function of the monetary policy authority for the annual time series period from 2002 to 2019 using nonlinear Taylor rule.Evaluating the behavior of monetary policy makers in response to changes in situational variables; Oil price changes, official exchange rate changes, inflation gap and production gap using smooth transition regression (STR) model have shown that, firstly: the reaction function of the monetary policymaker in Iran is non-linear and secondly; It can be seen that by entering the variables of official exchange rate changes and oil price changes into the model, with the increase of the production gap coefficient compared to the inflation coefficient, the inflation targeting scenario changes towards the targeting of production stabilization, and thirdly; The variable influence channel of oil price changes on the reaction function of the monetary policymaker is the official exchange rate gap.

Improving the level of social welfare is one of the main aims of countries. Various factors can affect social welfare the privatization is one of these factors. this study has investigated the effect of privatization on social welfare in Iran based on Amartya Sen social welfare index during the period 1991 to 2022 Using the smooth transition regression approach. The control variables of the research include trade openness, industrialization, energy consumption and carbon dioxide emissions. Based on the findings of the research, the optimal model is non-linear with 2 regimes and the transition from regime 1 to regime 2 has happened very gently. The results indicate that privatization before the threshold value of 2476.16 during 1991 before 2003 has a positive and significant effect on the social welfare index and after passing the threshold value during 2003 to 2022, the positive effect has decreased and gradually changed to a negative effect. Trade openness has no significant effect on social welfare in the first regime and has a negative and significant effect in the second regime. Industrialization and energy consumption variables had a negative and significant effect in the first regime and a positive and significant effect in the second regime.

Climate change is becoming a global crisis that can affect all aspects of human life on Earth, including the economy. So, protecting the environment and achieving sustainable development goals are now on the agenda of many governments. This article uses the Panel Smooth Transition Regression Model to test the role of information communication technology as a transition variable. In this research, it is investigated whether ICT can decouple the economic growth from the increase in pollution by changing the effect of productivity on CO2 emission. The goal is to show whether policymakers can use the development of the digital economy around the world to achieve better environmental and economic outcomes. This study was conducted on a global scale and data from 108 countries was used from 2003 to 2019. The results show that the co2 emission follows a PSTR model with ICT as a transition variable that changes the effect of total factor productivity on co2 emission in favor of the environment. ICT development will improve carbon efficiency and reduce climate change.

The relationship between nominal interest rates and inflation is one of the most important issues in macroeconomic issues. Knowing this relationship and knowing the direction of this relationship will have many benefits for all economic and monetary policymakers. In this study, by expanding the theory of quantity of money, we examine the relationship between nominal interest rates and inflation rates and test this relationship using the gentle transition regression approach during 1352-96. The results show that as interest rates rise (especially when the interest rate exceeds its threshold), its impact on inflation increases. Also, the effect of interest rates on the general level of prices does not have a severe effect and changes in parameters are slow. Therefore, it can be concluded that interest rate instruments cannot be used to control high inflation and the use of policies that reduce the speed of money circulation can be more effective in controlling the general level of prices. This result shows in general terms that in the long run, interest rate income that enters the economy from payment to the factors of production is practically compensated and eliminated by reducing the purchasing power of money due to the increase in the general level of prices in society. Perhaps this can be considered as one of the wisdoms that God Almighty has said in the Holy Qur'an about the sanctity of usury: "God forbid usury" means that God eliminates usury,cited.

The main objective of this research is to study the Taylor hypothesis (based on the role of the inflation environment) in Iran. For this purpose, seasonal time series data of the Iranian economy have been used during the 1988: Q1-2015: Q4 period and smooth transition regression model has been used. The empirical findings show that the import price in the high inflationary regime is lower than the low inflationary one, and Taylor's hypothesis is confirmed. The degree of exchange rate pass-through to import price index under the low inflation regime is 0. 30414 and 0. 09061 in short and long run, respectively. In a high inflation regime, it is 0. 58202, 0. 72016 respectively in short and long run. Therefore, inflation control policies can have a positive impact on reducing the exchange rate pass-through to the import price index.