The simplest measure of spread is the distance between extremes. Range is the difference between the highest and lowest values in a set of numbers. If test scores run from 62 to 98, the range is 36. The statistic is easy to calculate and gives a quick sense of how widely the data are scattered.

Its usefulness is limited. A single outlier can inflate the range dramatically, making a data set appear more variable than most of its members actually are. For that reason researchers often prefer the interquartile range or the standard deviation, both of which are less sensitive to extreme scores. Still, the range remains a transparent starting point, especially when communicating with audiences unfamiliar with more technical measures.

In practice the range appears in weather reports (high and low temperatures), sports statistics (highest and lowest scores), and quality-control charts. It answers a basic question: how far apart do the observations lie? When the answer matters more than precision about the middle of the distribution, the range supplies a direct and easily understood reply.