Chapter 09 – The Capital Asset Pricing Model
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81. Discuss the assumptions of the capital asset pricing model, and how these assumptions
relate to the “real world” investment decision process.
The assumptions are:
(a) The market is composed of many small investors, who are price-takers; i. e., perfect
competition. In reality this assumption was fairly realistic until recent years when institutional
(c) Investments are limited to those that are publicly traded. In addition, it is assumed that
investors may borrow or lend any amount at a fixed, risk-free rate. Obviously, investors may
(d) Investors pay no taxes on returns and incur no transaction costs. Obviously, investors do
pay taxes and do incur transaction costs. The tax differentials across different types of
investment income and across different income levels have been lessened as a result of the
income tax simplification of 1986. Obviously, investors should consider after-tax, not before-
tax, returns; however, the no-tax assumption of the model is not a serious departure from
(e) All investors are mean-variance efficient. This assumption implies that all investors make
(f) All investors have homogeneous expectations, meaning that given the same data all
investors would process the data in the same manner, resulting in the same risk/return
assessments for all investment alternatives. Obviously, we do not have homogenous