financial, invested in the firm. In this chapter, we will argue that risk in an equity
investment has to be perceived through the eyes of investors in the firm. Since firms like
Disney often have thousands of investors, often with very different perspectives, we will
go further. We will assert that risk has to be measured from the perspective of not just
any investor in the stock, but of the marginal investor, defined to be the investor most
likely to be trading on the stock at any given point in time. The objective in corporate
finance is the maximization of firm value and stock price. If we want to stay true to this
objective, we have to consider the viewpoint of those who set the stock prices, and they
are the marginal investors.
Finally, the risk in a company can be viewed very differently by investors in its
stock (equity investors) and by lenders to the firm (bondholders and bankers). Equity
investors who benefit from upside as well as downside tend to take a much more
sanguine view of risk than lenders who have limited upside but potentially high
downside. We will consider how to measure equity risk in the first part of the chapter and
risk from the perspective of lenders in the latter half of the chapter.
We will be presenting a number of different risk and return models in this chapter.
In order to evaluate the relative strengths of these models, it is worth reviewing the
characteristics of a good risk and return model.
1. It should come up with a measure of risk that applies to all assets and not be
asset-specific.
2. It should clearly delineate what types of risk are rewarded and what are not,
and provide a rationale for the delineation.
3. It should come up with standardized risk measures, i.e., an investor presented
with a risk measure for an individual asset should be able to draw conclusions
about whether the asset is above-average or below-average risk.
4. It should translate the measure of risk into a rate of return that the investor
should demand as compensation for bearing the risk.
5. It should work well not only at explaining past returns, but also in predicting
future expected returns.