In this article, at the first step, an attempt is made to examine is there any trends between two different alternate periods in order to understand the relationship between the previous beta with the future one. At the next step the goal is to study the stability of betas for individual stocks and portfolio of stocks. For this mean we analysis monthly returns of 85 companies over a period to 6 years (from 1997 to 2002). The results show that the stability of beta for individual stocks and portfolio of stocks can not be rejected.
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