scatter

The dispersion¹, scatter¹, variation¹ (150-3) or variability¹ of a set of observations depends on the differences² or deviations² (150-3) between its elements, Here the most common measures of dispersion³ only are mentioned. The range⁴ is the difference between the largest and the smallest value of a set of elements. The interquartile range⁵ is the difference between the first and third quartiles (cf. paragraph 142) and contains half the observations of the set. The semi-interquartile range⁶, also called the quartile deviation⁶, which is half the interquartile range, is often taken as a measure of dispersion. The mean deviation⁷ or average deviation⁷ is the arithmetic mean (140-2) of the positive values of the deviations of individual items from the average, the variance⁸ is the arithmetic mean of the squares of these deviations and the standard deviation⁹ is the square root of the variance.

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