How does rewriting the CAPM as a regression turn it into a test of alpha = 0, and why is Biogen's big alpha still not convincing?
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Transaction costs and an international CAPM
Record that transaction costs mainly slow rebalancing, and that a world CAPM assumes capital-market integration, which the Fama-French regional tests do not strongly support.
The CAPM as a regression with residual
Write , label its systematic and idiosyncratic parts, and state that has mean zero and vanishes in a large portfolio by the law of large numbers.
The test on Biogen and Motorola
Write the excess-return regression and the total-return intercept , then compute both stocks' alphas with a monthly and compare each with its standard error.