Considering the Tehran stock exchange’s status after the Covid-19 pandemic,it is essential to assess the role of different assets as a risk hedge and safe haven of the stock market during the pandemic. In this study, the trend of the gold and US dollar was evaluated and compared using EGARCH and quantile regression methods before (2018/6/19-2020/2/19) and after Covid-19 (2020/2/23-2021/10/12). According to the numerical results, although the Gold and US dollar performed very well as a safe haven for the stock market before Covid-19, they are not good safe havens in the Covid-19 pandemic. On the other hand, Gold has a positive relation with the stock market when the stock market collapses in the Covid-19 pandemic. Therefore, the gold is not an appropriate asset to hedge the risk of the stock market during the Covid-19 pandemic. However, the US dollar is better for stock market risk hedging in this period. Our results have revealed that the gold was a hedge for the stock market before Covid-19 pandemic. In this period, Gold had a negative relationship with the stock market in all conditions (except quantile 25% and 50%). Also, the US dollar could hedge the risk of the stock market before the Covid-19 pandemic in bearish, medium and bullish markets.

This article introduces the most popular tests statistics for stability of coeficients in econometrics. Main emphsits is on sheding a light on the advantages and disadvantages. of each test statistics and assumptions which have been based on. The present study consist of a wide range of test statistics from 1960 to 1999 for linear, non linear, simulation and single equations.

For the Estimation of econometric models a researcher is usually facing this question that which one of the linear or logaritmic linear model"s should be estimated and prefered. The present paper answers this important question by the introduction of MWD test and in case study by the introduction of Engel"s Curve. And about some of the essential commodities in Iran chooses prefered models in each case.

This paper examines the effectiveness of financial rewards on the production process of hot rolling mill in Mobarekeh Steel Complex. The authors hypothesize that the policy of financial rewards granting to personnel plays a positive and significant role to a certain extent in production effectiveness. It also postulates that rises in direct labour time, electricity and gas energies as well as machinery equipment and materials lead to an improvement in steel products that will be accepted by quality control unit and met with customer satisfaction.To analyze the impacts of such determinants on production, an econometric Cobb-Douglas production model is specified and estimated using monthly data over the period of 1372:1-1376:12.A dummy variable is employed in the model to indicate the effect of financial rewards on the production process, defining a policy for two separate periods in which workers mayor may not benefit from such rewards. Estimation results confirm that the hypothesis cannot be rejected and all explanatory variables have direct impacts on the dependant production variable.Finally, a scenario of a 10 percent increase in the direct labor time, as an alternative policy, is conducted to show its effect on the model through a simulation procedure. Results reveal that the production process of the hot rolling mill in Mobarekeh Steel Complex is substantially influenced.