Spread & Standard Deviation
Standard deviation measures how far the data are from the mean.
The rules
- A larger standard deviation means more spread.
- Range = maximum − minimum.
- Adding the same number to every value doesn't change the spread. Multiplying scales it.
- Compare spread, not just averages.
Watch out: Confusing the standard deviation with the mean.
Worked example
Data set A is 4, 5, 6. Data set B is 1, 5, 9. Which has the greater standard deviation?
- Both have mean 5.
- B's values are farther from the mean.
Answer: B
Try it yourself
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