62 CHAPTER 2 Exploring Data with Tables and Graphs Key Concept Section 2-2 introduced the histogram, and this section introduces other common graphs that foster understanding of data. We also discuss some graphs that are deceptive because they create impressions about data that are somehow misleading or wrong. The era of charming and primitive hand-drawn graphs has passed, and technology now provides us with powerful tools for generating a wide variety of graphs. Here we go. Graphs That Enlighten Dotplots A dotplot consists of a graph of quantitative data in which each data value is plotted as a point (or dot) above a horizontal scale of values. Dots representing equal values are stacked. Features of a Dotplot ■ Displays the shape of the distribution of data. ■ It is usually possible to recreate the original list of data values. 2-3 Graphs That Enlighten and Graphs That Deceive Dotplot of Pulse Rates of Males EXAMPLE 1 Figure 2-6 shows a dotplot of the pulse rates (beats per minute) of males from Data Set 1 “Body Data” in Appendix B. The two stacked dots above the position at 50 indicate that two of the pulse rates are 50. (In this dotplot, the horizontal scale allows even numbers only, but the original pulse rates are all even numbers.) For instructional purposes, this dotplot includes a fictional pulse rate of 10 beats per minute which is not part of the original data set. The lowest pulse rate ever recorded in a living healthy person is 28 beats per minute, so this value is clearly an error. In this case, the pulse rate of 10 beats per minute is an outlier, because it is very far from the other data values. See how that outlier becomes easy to identify when included as part of the dotplot. In this example, the dotplot allows us to see that the general shape of the distribution is approximately normal, and there is an outlier present. YOUR TURN. Do Exercise 5 “Pulse Rates.” FIGURE 2-6 Dotplot of Pulse Rates of Males G D The Power of a Graph With annual sales around $13 billion and with roughly 50 million people using it, Pfizer’s prescription drug Lipitor (generic name, atorvastatin) has become the most profitable and most widely used prescription drug ever marketed. In the early stages of its development, Lipitor was compared to other drugs (Zocor [simvastatin], Mevacor [lovastatin], Lescol [fluvastatin], and Pravachol [pravastatin]) in a process that involved controlled trials. The summary report included a graph showing a Lipitor curve that had a steeper rise than the curves for the other drugs, visually showing that Lipitor was more effective in reducing cholesterol than the other drugs. Pat Kelly, who was then a senior marketing executive for Pfizer, said, “I will never forget seeing that chart . . . . It was like ‘Aha!’ Now I know what this is about. We can communicate this!” The Food and Drug Administration approved Lipitor and allowed Pfizer to include the graph with each prescription. Pfizer sales personnel also distributed the graph to physicians. W s $ w 5
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