Standard deviation is not a range. It is a single number that represents how much the data is a set of observations varies about the mean. Mathematically it is the square root of the sum of the squares of the differences between the samples and the mean divided by N, or divided by N-1. The decision of N or N-1 depends on whether or not the mean was also calculated with the calculation of the standard deviation. If it was the same calculation, use N-1, it the mean was known beforehand, use N.
For clarification of parenthesis, and use of N or N-1, see the Related Link below.
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The range is 9 and 3.01 is the standard deviation.
The range is 12 and the standard deviation is 3.822448314.
The standard deviation is better since it takes account of all the information in the data set. However, the range is quick and easy to compute.
Standard deviation shows how much variation there is from the "average" (mean). A low standard deviation indicates that the data points tend to be very close to the mean, whereas high standard deviation indicates that the data are spread out over a large range of values.
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