Measures of Variability
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0000
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Abstract
Although statistics that indicate the center of a score distribution provide useful and important information about a group of scores, they certainly don't give a complete picture of the distribution. Two score distributions that have identical means, medians, and modes, such as those shown in Figure 3.1, can still differ from each other in important ways. The distributions shown in Figure 3.1 are identical in their central tendencies. In addition, both are symmetric and both are unimodal. They differ only in the spread of their scores, the extent to which the scores differ or vary.
Description
This chapter discusses how scores can differ in their spread despite having identical central tendencies. It introduces key measures of variability: range, interquartile range, semi-interquartile range, variance, and standard deviation. The importance of variability in understanding group differences is emphasized. It also explains how the shape of distribution affects the choice of variability measure.
Keywords
Interquartile Range (IQR), Standard Deviation, Normal Distribution, Skewness, Semi-Interquartile Range (Q)