The Capital Asset Pricing Model

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2.1 The Capital Asset Pricing Model

The CAPM is one of the most influential theories in finance, and it is widely used in applications (e.g. estimating the cost of the capital for firms) . Meanwhile, the CAPM is probably the most tested model. The beauty of the CAPM comes from its parsimony and elegance in establishing a linear relationship between risk and return. The CAPM indicates that if an investor wants to obtain a higher expected rate of return, he has to bear additional risk. It is derived on the basis of the mean-variance approach, which is first proposed by Markowitz (1959). The mean-variance approach claims that mean is a proxy of the asset’s return and variance stands for the risk which the asset bears. If two assets have the same return, the investor will choose to invest in the asset with lower degree of risk. If two assets have the same degree of risk, the investor will choose to buy the asset with higher return.

Sharpe (1964) is the first one who applies the mean-variance approach to construct a market equilibrium theory about asset prices under conditions of risk. First, Sharpe defines investor’s utility function with only two parameters – the expected value and standard deviation.

U=f(E_w,σ_w)

where E_w is the expected future wealth and σ_w indicates the predicted standard deviation of the possible divergence of actual future wealth from the expected future wealth E_w. Thus, for risk-averse investors, dU⁄(dE_w )>0 and dU⁄(dσ_w )<0. In the presence of two risky assets, the investment opportunity curve is determined by assets’ expected rate of return, risk and the correlation between different assets. The same analysis also applies to determining the utility of an investor who invests in the combination of ri...

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