Objective: Stock markets are extremely volatile and contain only a small predictable component that may still be economically justifiable and could be translated into substantial utility gains for a risk-averse investor. Moreover, the degree of return predictability varies over time and the predictive power of some instruments appears to be diminishing in recent decades. Presumably, the structural relationship between economic predictor variables and future stock returns is time-varying or regime-dependent. Identifying the prevailing macroeconomic state and risk regime is thus highly beneficial for meaningful portfolio management. Therefore, the purpose of this paper is to develop a model for switching regimes in the Tehran Stock Exchange (TSE) index return and to determine the transit variables among economic and financial variables. Methods: The approach used in this paper is based on the smooth transition regression model. Therefore, the statistical data of the 2006-2019 period were used, based on the frequency of seasonal data for TEDPIX returns and economic and financial variables including inflation rate, interest rate, GDP, exchange rate, oil price, money supply, priceto-earnings (P/E) ratio, and price-to-book (P/B) ratio. Results: The fitted model showed that the rate of return on the Tehran Stock Exchange index continuously switches from a lower inefficient regime to an upper inefficient one. This study confirmed the relationship between explanatory variables and stock returns is nonlinear and the existence of multiple regimes governing the, return of the TSE index as well as the importance of accounting for nonlinearity and the cyclical behavior of stock returns. Conclusion: According to the obtained results index returns and explanatory variables have a nonlinear and asymmetric relationship and among the explanatory variables of economic and financial, the exchange rate is a transition variable. The regression coefficients during the establishment of the low fluctuations regime and higher fluctuations regime are different. Same as previous studies, the current analysis featured a range of important financial and macroeconomic factors for determining the behavior of stock returns. The results provided evidence that the real significance of the influence of factors such as exchange rate is only revealed once regimes are explicitly modeled.

Forecasting business cycles is very important in macroeconomic and it is an important part in process of economic decision-making and policy. In recent years, non-linear models have been considered more for forecasting economic variables and application of these models has been made a significant improvement in modeling of the behavior of variables in the area of macroeconomic and particularly financial economics. This article provides a convenient and powerful model for forecasting business cycles by using smooth transition regression (STR). The results show that very little error that indicates model performance is acceptable.

Based on transaction cost theory, active management leads to a reduction in transaction costs and thus reduction in the distance between the bids and ask gap. On the contrary, based on the adverse selection hypothesis, when a group of shareholders has the advantage of information over another, there is an information asymmetric which in turn will reduce liquidity. This study is primarily aimed at testing the mentioned theories. Using a panel smooth transition regression model, as a new econometric technique, we examined the data to explore the asymmetric impact of blockholders ownership on liquidity in the 148 firms for the period 2009 to 2018 from TSE. Our empirical results strongly rejected the null hypothesis of linearity, and the test on inexistence of nonlinearity indicated a model with one transition function and two threshold parameters. The first regime (levels of blockholders ownership below 36. 1 percent) showed that liquidity increases with institutional ownership while the trend was reversed in the second regime (levels of blockholders ownership above 36. 1 percent). Blockholders are inherently good or bad for the capital market because their impact varies from diet to regimen, and it seems to be dependent on the percentage of ownership of blockholders and corporate characteristics.

This paper examines the asymmetric effect of inflation on the economic growth in Iran during the period 1990:2–2008:2. To that end, we use a smooth transition regression model which allows having a regime change in the relationship between the variables.We found evidence of threshold behavior in the relationship between the inflation rate and the economic growth in Iran; such that, there is a threshold level of inflation which beyond that the relationship between these variables changes. This estimated threshold for the quarterly inflation rate is 4.56. The results also show that there is a positive contemporaneous relationship between the inflation rate and the economic growth in the first regime, where the inflation rate is below 4.56; however, for the periods with an inflation rate higher than 4.56 there is not any significant relationship between the inflation rate and the economic growth. In addition, the effects of the government expenditures and investment are regime-dependent and change over the time.

The Phillips curve usually has been estimated in a linear framework which implies a stable constant relationship between inflation and unemployment. Some of the studies claim that the slope of the Phillips curve is a function of macroeconomic conditions and also the relationship is asymmetric. This article deals with a smooth transition regression model for relationship between inflation and unemployment for Iran, during the period of 1971 -2007. smooth transition regression model is a non linear time series regression model which could be considered as developed form of regime switching regression model. Results show that there is a negative and nonlinear relationship between inflation and unemployment in short-term. Regarding this result it's highly important for policy makers to be able to make a relationship between these two variables.

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.

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.