PFE, Chapter 10: What is risk? page 2
a financial presentation, we look skeptical and say “Have you considered the risks?” Usually
that’s enough to score a point or two.
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Our intuition usually relates financial risks to unpredictability. A financial asset like a
savings account is thought to be not risky because its future value is known, whereas a financial
asset like a stock is risky because we do not know what it will be worth in the future. Financial
assets of different types have different gradations of risk: Our intuitions tell us that a savings
account is less risky than a share in a company, and a share in a high-tech start-up is more risky
than a share in a well-established blue-chip company.
The intuition which ties unpredictability and risk together is valid, but can have some
surprising aspects. For example, in section 10.??? we show that a Treasury bill, a bond issued by
the United States government, can sometime be risky. The T-bill becomes risky if you need to
sell it before it matures. We illustrate this risk with an example. We also look at the risk of
holding a share, and show that it can be quantified statistically. This is an important insight for
Chapters 11-15, where we use a statistical description of stock price risk to talk about choosing
portfolios of stocks.
Although we have tried to make the chapter unstatistical and non-mathematical,
inevitably the measurement of risk involves calculations.
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I give my students the following hint about taking finance exams: Suppose you have to answer a question to which
you absolutely don’t know the answer (“What is the zeta function of the annual returns?” “How do you explain the
difference between XYZ Corp’s annual returns over time?”). If you know nothing about the question, make up a
meaningless sentence which includes the word “risk” (“The zeta function of the annual returns relates to the
riskiness of the returns.” “XYZ’s annual returns vary because of the changing risk of the company.”) You’re bound
to get a point or two.