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Measures of dispersion indicate how much the data in a given set of numerical data are spread out.
The range is the distance between the largest and the smallest value in the data set. Of all measures of dispersion, the range is most sensitive to outliers. In a sense, the interquartile range is the range of the middle half of the data. Although more difficult to compute than the other measures of dispersion, the standard deviation and the variance are the most useful ones. This is largely due to their nice mathematical properties.