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CAPM

CAPM process just chooses the best possible and efficient portfolio that has been derived based on expected returns, as this model assumes that all investors are averse to risk. As the model measures risk through deviation of asset returns, many factors like inflation, which affect the portfolio returns are not considered. In addition, the asset returns can be irregular while calculating in real practice. However, the CAPM model assumes the asset returns to be normally distributed. Real world distribution of such returns is non-normal. (Limitations of CAPM, 2012) Investment costs also differ according to the ability of the investors to invest in the required portfolio. Accordingly, it is impractical to assume that security returns will remain identical for CAPM to determine the most efficient portfolio for the investors. Similarly, risk taking ability and preference varies among investors, as many may choose low risk securities and some may go for high risk ones. In addition, there are many assumptions, which may not be correct for the process of application of CAPM. Finding a risk free security remains the favorite dream of many investors. However, in realty there is nothing as risk free investment. The government short-term security is considered the most liquid with least risk, as governments are unlikely to default. However, the inflation plays the spoilsport, as it is related to return variance. The borrowing and lending rates also differ and may not be uniform, since the markets may

not behave according to pre-set assumptions. CAPM application is based on such assumptions, which cannot work in real world. (Limitations of CAPM, 2009) Roll’s critique of early empirical test of the CAPM After the development of CAPM, many tests were conducted to ascertain the accuracy of this application in predicting the correct asset values. The tests were based on proxy values for different variables. However, in most of the cases, CAPM could not predict the accurate asset values and it did not prove suitable for such predictions. In the year 1977, Richard Roll opined that CAPM could not be tested empirically, although it may prove valid theoretically. The reason for this, according to Roll is the variation in stock indexes, which may not prove good proxies for CAPM variables.(Taylor, 2005) In the CAPM formula: E(Ri) =RF +?i [E(RM) - RF ], ‘Beta i’ represents the systematic risk for security ’i’, while ‘RF’ means the risk free return and E(Ri) represents the expected return on security ‘i’. Roll criticized this formula arguing that the index portfolio used here for estimation of ‘betas’ is based on the assumption of efficient property of securities. However, the CAPM does not assert the true market portfolio being an efficient one. The mathematical fact mentions that expected return from a security has linear relation with the systematic risk, and portfolio returns and betas have also similar relationship. The basis of this calculation is the efficient set of index portfolio. CAPM assumptions, according to Roll do not hold good here. Roll has opined that it is impossible to test the CAPM validity, since it is related to the efficiency of market portfolios and it may not be possible to observe the investment opportunities based on their expected returns. (The main theoretical limitations of CAPM) CAPM vs. APT Arbitrage is involved when an investor gets return on a zero beta investment portfolio, which is greater than any

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