evaluation of risk and return and effect of stock transactions amount on risk and return in food, pharmaceutical and chemical industries to assess the rationality of market behavior

in this research, the risk, return and coefficient of variation (cv) are calculated and compared in the food, pharmaceutical and chemical industries during 2003-2008 in tehran stock exchange. also, the effect of stock transactions is investigated in the companies working in these industries to realize the risk, return and cv.  results of this research represent that there are no significant relationship (95% of significance) between risk, return and cv and the amount of stock transactions. according to the rational market behavior, usually by an increase in the size of transaction, there should be an increasing trend in risk and return, but, in this research, the opposite are found. so, the findings point out that the market‘s behavior is irrational.