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During the 1960s,
Eugene Fama developed his
efficient
market hypothesis and
William Sharpe published his
capital asset pricing
model (CAPM). The latter proved important for empirically confirming the
former.
CAPM states that assets' expected
returns depend on
their systematic risk. Those with greater systematic risk have higher
expected returns than those with lower systematic risk. This means an
investment manager can boost his returns by merely increasing the
systematic risk (beta) of his portfolio—which has nothing to do with his
ability to time the market or pick stocks. Early studies of investment
manager performance—including Cowles (1933), Friend et al (1962) and
Horowitz (1963)—were flawed because they assessed managers' returns
without any adjustment for risk.
Not only did CAPM highlight this problem, it provided a
framework for assessing—and hence adjusting returns for—a portfolio's
risk. Between 1965 and 1970, a number of papers were
published on investment managers' performance, and these suggested
various risk-adjusted performance metrics
(RAPM) based on CAPM. Jack
Treynor (1965) proposed that managers' risk-adjusted performance be measured as
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[1] |
Sharpe (1966) proposed a
metric with the same numerator but a
different denominator. He felt it appropriate to penalize a portfolio
manager for not fully
diversifying, so his metric was
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[2] |
where the denominator is generally calculated as the
standard deviation of
simple return.
Formulas [1] and [2] have come to be known,
respectively, as the Treynor ratio and the
Sharpe ratio. Both have been
widely adopted by practitioners for performance assessments. The Sharpe
ratio is the more popular of the two.
In 1968, Michael Jensen published a RAPM that proved
even more popular than the Sharpe ratio. Today, it is more than a RAPM.
For proponents of active portfolio management, it symbolizes
their belief in the ability of active managers to outperform the overall
market. Its name is Jensen's alpha.
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Is
it possible for the Treynor ratio to ever take on a negative
value? If so, how might we interpret such a result?.
[solution]
Is
it possible for the Sharpe ratio to ever take on a negative
value? If so, how might we interpret such a result?.
[solution] |
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Cowles,
Alfred 3rd (1933). Can stock market forecasters forecast?
Econometrica, 1 (3), 309-324.
Friend,
Irwin, F. E. Brown, Edward S. Herman, and Douglas Vickers
(1962). A Study of Mutual Funds: Investment Policy and
Investment Company Performance, Report to the Committee on
Interstate and Foreign Commerce, House Report no. 2274, 87th
Congress, Second Session.
Horowitz,
Ira (1963). The varying (?) quality of investment trust
management, Journal of the American Statistical Association,
58 (304), 1011-1032.
Sharpe,
William F. (1966). Mutual fund performance, Journal of
Business, 39 (1) Part 2, Supplement, 119-138.
Treynor,
Jack (1965). How to rate management of investment funds,
Harvard Business Review, 43 (1), 63-75. |
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