Chapter 4 Describing Your Data 159Measures of Variability
The mean and median do not tell the whole story about a distribution. It’s also
important to take into account the variability of the data. Variability is a measure
of how much data values differ from one another, or equivalently, how widely
the data values are spread out around the center. Consider the pair of histograms
shown in Figure 4-20. The mean and median are the same for both distributions,
but the variability of the data is much greater for the second fi gure.Figure 4-20
Distributions
with low and
high variability
The simplest measure of variability is the range, which is the difference
between the maximum value in the distribution and the minimum value.
A large variability usually results in a large range of values. However,
the range can be a poor and misleading measure of variability. As shown in
Figure 4-21, two distributions can have the same range but be very different
in the variability of their data.