A study of the effects of company size on systematic risk based on the capital asset pricing model among accepted companies in Tehran Stock Market ,

Systematic risk (beta) is one of the most effective factors in predicting the appropriate required rate of return of portfolios. Understanding systematic risk of usual portfolio of various companies helps investors consider financial investment, more confidentially. The aim of this study is to determine if there is any significant relationship between Company Size (Market value of stocks, Book value of stocks, level of company sale, trade volume of stocks, Price dividend ratio) as independent variables and Systematic risk (Beta) as dependent variables. The study chooses 112 companies accepted in Tehran Stock Market based on screening (systematic deletion) in a six-year- period from 2005 to 2010. The required data were gathered from basic financial statement, committee reports, and other available documents in Tehran Stock Market. Regression and Pearson correlation were used to analyze the data. The results of the study revealed that there is a significant relationship between the variables. Some suggestions regarding the topic of the research are given too