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Figure 3.8: Returns and Betas: Ten Worst Months between 1926 and 1991

□ High-beta stocks □ Whole Market □ Low-beta stocks

While the initial tests of the APM and the multi-factor models suggested that they might provide more promise in terms of explaining differences in returns, a distinction has to be drawn between the use of these models to explain differences in past returns and their use to get expected returns for the future. The competitors to the CAPM clearly do a much better job at explaining past returns since they do not constrain themselves to one factor, as the CAPM does. This extension to multiple factors does become more of a problem when we try to project expected returns into the future, since the betas and premiums of each of these factors now have to be estimated. As the factor premiums and

16 Chan, L.K. and J. Lakonsihok, 1993, Are the reports of Beta's death premature?, Journal of Portfolio betas are themselves volatile, the estimation error may wipe out the benefits that could be gained by moving from the CAPM to more complex models. The regression models that were offered as an alternative are even more exposed to this problem, since the variables that work best as proxies for market risk in one period (such as size) may not be the ones that work in the next period. This may explain why multi-factor models have been accepted more widely in evaluating portfolio performance evaluation than in corporate finance; the former is focused on past returns whereas the latter is concerned with future expected returns.

Ultimately, the survival of the captial asset pricing model as the default model for risk in real world application is a testament both to its intuitive appeal and the failure of more complex models to deliver significant improvement in terms of expected returns. We would argue that a judicious use of the capital asset pricing model, without an over reliance on historical data, in conjunction with the accumulated evidence17 presented by those who have developed the alternatives to the CAPM, is still the most effective way of dealing with risk in modern corporate finance.

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