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Development of financial markets plays a major role in economic development. The present study estimates the effect of inflation on the relationship between financial development and employment using STR smooth transition regression model in Iran during 1992-2014. The results show that when inflation increases beyond threshold level, quasi-money negative effects on unemployment rate are intensified, and an increase in quasi-money has greater effect on increase in employment. Furthermore, increase in inflation rate and passing threshold level, and increase in capital market volume and domestic credit granted to private sector result in decreasing employment rate. The effect of monetary base on unemployment rate is positive in both regimes, but higher inflation (passing the threshold level of inflation) has intensified the positive effect of monetary base on unemployment rate. In other words, an increase in inflation rate has increased the monetary base, which in turn has reduced the employment level.

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The relationship between financial decentralization and economic growth has been one of the crucial issues in economics in recent decades. Financial decentralization could affect economic growth and consequently development programs and the expansion of regional balance policies. This study investigates the nonlinear behavior of economic growth and financial decentralization in the Iranian provinces during the period 2004-2016 using a panel smooth transition regression model as one of the prominent models of regime change. A hybrid financial decentralization index is extracted using the principal component analysis technique and it is used as a transfer variable to study the changes in economic growth in the nonlinear model. Results of estimation confirm a nonlinear relationship between the variables under study and propose a dual-regime model with a threshold of 3.1941 and a slope parameter of 4.2869. So, the effect of combined financial decentralization on growth of the provinces is asymmetric. Thus, with increasing decentralization in the first regime, economic growth becomes positive and after crossing the threshold and entering the second regime, it becomes negative due to the costs associated with increasing financial decentralization. Therefore, the relationship between hybrid financial decentralization and the economic growth of the provinces can be shown as an inverse parabola.

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The relationship between exchange rate changes and trade balance has always been one of the major issues in theoretical literature and policy circles. A new approach to theoretical literature and empirical work suggest that the interaction of these two variables depends on a number of issues, including how each country's export and import markets interact, and the degree to which exports of goods are dependent on imports. For this purpose, in the paper, the relationship between exchange rate and trade balance in the Iranian economy is examined by considering the crucial role of Intra –industry trade in the form of smooth transition regression model for the period 2001: 4 to 2018: 4. The results showed that the coefficient of effect of the exchange rate on the trade balance in each period is affected by the intra--industry index, so that the lower the index, the less the effect of the exchange rate increase on the trade balance, and as this index improves, the impact is greater. This means that the positive effects of money devaluation on the trade balance can be benefited when the competitiveness of domestic products with similar foreign goods in each sector increases.

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In this study, a new composite index, called the SWI (Sustainable Welfare Index) is proposed to assess "sustainable welfare". This index consists of significant social, economic, and environmental variables in flow and monetary forms, and can be directly compared to the GDP. Despite the paucity of statistical data, an attempt has been made to make a relative assessment of sustainable welfare in the Iranian economy during the years 2004 to 2018. According to the comparison of calculated SWI with GDP, it has been shown that the two indicators have similar movements and higher correlations in the period under study. In addition, despite the availability of economic growth during the period, society has been below a sustainable welfare level. In this study, the threshold effect of three SWI sub-indices on the total index was assessed using the smooth transition regression (STR) Model. As a result, the sub-index "Social Expenditure" through changes in "welfare losses due to income inequality" is of threshold effect on SWI.