Understanding Risk and Return, the CAPM,
and the Fama-French Three-Factor Model
RISK AND RETURN
The General Concept: Higher Expected Returns Require Taking Higher Risk
Most investors are comfortable with the notion that taking higher levels of risk is necessary to
expect to earn higher returns. In this note, we explain two important models that have been
developed to make this relationship precise. Then we explain how such tools can be used by
investors to evaluate assets such as mutual funds.
Why should riskier companies have higher returns? Intuitively, an investor would require a
higher expected return in exchange for accepting greater risk. And, we do, in fact observe this
relationship when we look back at historical long-run returns of stocks, bonds, and less risky
securities as shown in the first chart.
To understand this, imagine an investment that is expected to generate $1 million per year in
perpetuity. How much is someone likely to pay for such an asset? The answer depends on the
uncertainty or riskiness of the cash flows. With complete certainty that the cash flows will all be
paid when promised, an investor would discount the asset at the risk-free rate. As the degree of
uncertainty increases, the return required to justify the risk will be much higher, resulting in a
much lower price the investor would be willing to pay, simply because of the higher required
Furthermore, economists have made the assumption that investors are risk-averse, meaning that
they are willing to sacrifice some return (and accept even less than the expected present value of
the future returns) to reduce risk. If this assumption is true, we would expect investors to
demand a higher return to justify the additional risk accepted by holders of riskier assets.
This case note was written under the direction of Kent Womack and Ying Zhang by Adam Borchert, Lisa Ensz, Joep
Knijn, Greg Pope, and Aaron Smith. We would...