Interquartile Range

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The interquartile range is a measure of variability, spread or dispersion. It is the difference between the 75th percentile (often called Q3) and the 25th percentile (Q1). The formula for interquartile range is therefore: Q3-Q1. It is sometimes called the H-spread. although not used extensively, the interquartile range is a stable measure of spread and perhaps should be in more common usage.