In the analysis of the stock market and its market indices, instead of estimating returns and their distributions at a given time interval, it is possible to extract optimal time to achieve a certain return. In this study, the distribution of investment horizons and optimal investment horizons through inverse gamma statistics method for the indices of automobile, sugar, pharmaceutical, financial and banks industries in Tehran Stock Exchange were extracted, analyzed and compared. The results of the research show that at the levels of access to +5 percent return, automotive, sugar , banking and financial indices have shorter horizons than the total index, while in terms of access to negative returns ,the only indicator of the drug group has a longer horizon than the total index.
The existence of a stable source of income for the government is crucial for the financing of current and development expenditures. The major revenues of the government in Iran are derived from two sources of tax and oil revenues. Given that much of the oil revenue fluctuations are outside the control of domestic policymakers, it is better to focus on tax revenues in order to earn relatively stable revenues. However, tax revenues are also affected by cycles of boom and recession, and in terms of economic downturns, it is also difficult to earn money from this source. Thus, the solution for this problem is that the total tax revenue of the country is considered as a portfolio of income and applied to the methods of the financial economics to optimize it, in this way, an optimal combination Tax will be specified. Accordingly, in this study, by collecting information on different government revenues during the period of 1971-2017 and using the Markovitz model from two approaches to minimize risk and maximize returns, the optimal contribution of different tax bases for Iran has been calculated. The results show that the current share of the tax revenue base of the country is different from the optimal share
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