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CFA Level I · CFA Level I Exam · Statistical Characteristics of Asset Returns

A return distribution has a mean of 8% and a standard deviation of 5%. Using Chebyshev's inequality, the minimum percentage of observations lying within the interval from -2% to 18% is closest to:

At least 75% of observations lie in the interval. The range from -2% to 18% is the mean plus or minus 10%, which is two standard deviations. Chebyshev's inequality gives 1 minus 1/k squared, or 1 minus 1/4, equal to 75%, for any distribution.

  1. A68%
  2. B75%Correct
  3. C89%

Explanation

The interval 8% ± 10% is 2 standard deviations (10/5). Chebyshev gives at least 1 - 1/k² = 1 - 1/4 = 75%. The 68% figure is the normal-distribution value for one standard deviation, and 89% corresponds to k = 3.

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