See why equal means can hide different variability and what standard deviation summarizes.
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First lesson in this subject: Read data before calculating
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A contains 4, 5, 6; B contains 0, 5, 10. Both means are 5, but B’s observations lie farther apart. A center alone cannot describe this difference.
The range is largest minus smallest: 2 for A and 10 for B. It uses only the endpoints. A measure that uses every observation can describe spread more fully.
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First lesson in this subject: Read data before calculating
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Practice · Reason about averages, medians, spread and outliers. Change a data value to see which conclusions still hold.
Book · Read distributions, question samples, and explore how groups and outliers change a conclusion.
Previous lesson · Compare the mean and median, then explain what an unusually large value changes.
Next lesson · Distinguish chance differences between random samples from systematic selection bias.
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