| Standard deviation |
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| • | If
the population is normally distributed, |
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| you
can estimate the percentage of the |
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| population
within 1, 2, and 3 standard |
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| deviations
of the mean: |
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| • | 68%
of cases lie +/- 1 s.d. of mean |
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| • | 95%
of cases lie +/- 2 s.d.’s of mean |
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| • | 99.9%
of cases lie +/- 3 s.d.’s of mean |
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