56 CHAPTER 2 Exploring Data with Tables and Graphs FIGURE 2-3 Relative Frequency Histogram of Commute Time in Los Angeles from Table 2-1 FIGURE 2-2 Histogram of Commute Time in Los Angeles from Table 2-1 Critical Thinking: Interpreting Histograms Even though creating histograms is more fun than human beings should be allowed to have, the ultimate objective is to understand characteristics of the data. Explore the data by analyzing the histogram to see what can be learned about “CVDOT”: the center of the data, the variation (which will be discussed at length in Section 3-2), the shape of the distribution, whether there are any outliers (values far away from the other values), and time (whether there is any change in the characteristics of the data over time). Examining Figure 2-2, we see that the histogram is centered roughly around 30 minutes, and the shape of the distribution is a bit lopsided. Common Distribution Shapes The histograms shown in Figure 2-4 depict four common distribution shapes. FIGURE 2-4 Common Distributions (a) (c) (b) (d)
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