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In the previous section, we discussed measures of centrality, which provide information about the location of the center of frequency distributions of the data sets under consideration. For example, consider the frequency distribution curves shown in Figure 2.5.2. Measures of central tendency do not portray the whole picture of any data set. For example, it can be seen in Figure 2.5.2 that the two frequency distributions have the same mean, median, and mode. Interestingly, however, the two distributions are very different. The major difference is in the variation among the values associated with each distribution. It is important, then, for us to know about the variation among the values of the data set. Information about variation is provided by measures known as measures of dispersion. In this section, we study three measures of dispersion: range, variance, and standard deviation.

Figure 2.5.2 Two frequency distribution curves with equal mean, median, and mode values.