Variability in One Population and in Two Populations

Abstract

The expression, “A chain is only as strong as its weakest link,” may be construed as an admonition to consider the variability of the links as well as their average strength. In comparing distributions, averages alone are not always adequate. Figures 3.5 and 3.6 show two telephone waiting-time distributions with equal means (1.1 seconds) but very different shapes. In Section 4.3 we pointed out that their Standard deviations, 0.41 second and 0.69 second, were quite different. If the pupils in each of two school classes have mean IQs of 100, but Class A has a Standard deviation of 10, while Class B has a Standard deviation of 20, teaching the relatively homogeneous Class A may be very different from teaching the relatively heterogeneous Class B.