SAT and ACT math terms · SAT Math, ACT Math
Standard deviation
Standard deviation: A measure of spread showing how far data values typically are from the mean.
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What it means
A small standard deviation means values cluster near the mean; a large one means they are spread out. On the SAT and ACT, the usual task is to compare spreads by looking at how tightly values gather around the center.
Range, the difference between the maximum and minimum, is another measure of spread, but it depends only on two values.
Example
Set A: 9, 10, 10, 11. Set B: 2, 6, 14, 18. Both have mean 10, but set B has a much larger standard deviation.
On the exam
Expect to compare the standard deviations of two data sets or describe how a change affects spread.