Section 2.3 More Graphs for Quantitative Data 67 Solution Figure 2.16 presents the results. It is clear that vehicles driven at high altitude tend to produce higher emissions. High Altitude Sea Level 0 3 5 5 6 6 9 9 9 9 9 8 5 1 1 0 1 1 1 1 1 1 2 2 2 2 3 3 3 3 4 4 5 5 5 6 6 6 8 8 9 9 7 4 1 1 0 2 1 1 1 2 4 5 5 6 7 7 7 8 8 6 3 3 0 1 1 1 3 3 4 5 5 5 6 7 8 7 4 4 4 0 2 6 9 8 6 6 6 3 3 5 9 5 5 3 3 6 6 6 6 3 7 9 7 8 5 2 1 9 Figure 2.16 Back-to-back stem-and-leaf plots comparing the emissions in vehicles driven at high altitude with emissions from vehicles driven at sea level Objective 2 Construct dotplots Dotplots A dotplot is a graph that can be used to give a rough impression of the shape of a data set. It is useful when the data set is not too large, and when there are some repeated values. As an example, Table 2.18 presents the number of children of each of the presidents of the United States and their wives. Table 2.18 Numbers of Children of U.S. Presidents and Their Wives 0 2 10 2 5 3 6 2 2 4 1 5 4 15 3 4 5 3 2 3 4 2 6 0 0 0 8 3 3 6 2 4 2 0 4 6 4 7 2 0 1 2 6 Figure 2.17 presents a dotplot for the data in Table 2.18. For each value in the data set, a vertical column of dots is drawn, with the number of dots in the column equal to the number of times the value appears in the data set. The dotplot gives a good indication of where the values are concentrated, and where the gaps are. For example, it is immediately apparent from Figure 2.17 that the most frequent number of children is 2, and only four presidents had more than 6. (John Tyler holds the record with 15.) 0 5 10 15 Figure 2.17 Dotplot for the data in Table 2.18 EXAMPLE 2.15 Constructing a dotplot with technology Use technology to construct a dotplot for the exam score data in Table 2.16 on page 65.
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