Chapter 2: Graphs, Charts, and Tables--Describing Your Data

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64 CHAPTER 2 • GRAPHS, CHARTS, AND TABLES—DESCRIBING YOUR DATA SUMMARY Constructing Pie Charts A pie chart is constructed using the following steps: 1. Define the categories for the variable of interest. 2. For each category, determine the appropriate measure or value. The value assigned to each category is the proportion the category is to the total for all categories. 3. Construct the pie chart by displaying one slice for each category that is proportional in size to the proportion the category value is to the total of all categories. EXAMPLE 2-8 Pie Charts Gold Equipment A survey was recently conducted of 300 golfers that asked questions about the impact of new technology on the game. One question asked the golfers to indicate which area of golf equipment is most responsible for improving an amateur golfer’s game. The following data were obtained: TRY PROBLEM 2.28 Equipment Frequency Golf Ball 81 Club Head Material 66 Shaft Material 63 Club Head Size 63 Shaft Length 3 Don’t Know 24 To display these data in pie chart form, use the following steps: Step 1 Define the categories. The categories are the six equipment-response categories. Step 2 Determine the appropriate measure. The appropriate measure is the proportion of the golfers surveyed. The proportion for each category is determined by dividing the number of Club Head Size 21% Don’t Know 8% Shaft Length 1% Golf Equipment Impact Golf Ball 27% Shaft Material 21% Club Head Material 22%
CHAPTER 2 • GRAPHS, CHARTS, AND TABLES—DESCRIBING YOUR DATA 65 golfers in a category by the total sample size. For example, for the category golf ball, the percentage is 81/300 0.27 27%. Step 3 Construct the pie chart. The pie chart is constructed by dividing a circle into six slices (one for each category) such that each slice is proportional to the percentage of golfers in the category. Pie charts are sometimes mistakenly used when a bar chart would be more appropriate. For example, a few years ago the student leaders at Boise State University wanted to draw attention to the funding inequities among the four public universities in Idaho. To do so, they rented a large billboard adjacent to a major thoroughfare through downtown Boise. The billboard contained a large pie chart like the one shown in Figure 2.15, where each slice indicated the funding per student at a given university. However, for a pie chart to be appropriate, the slices of the pie should represent parts of a total. But in the case of the billboard, that was not the case. The amounts merely represented the dollars of state money spent per student at each university. The sum of the four dollar amounts on the pie chart was a meaningless number. In this case, a bar chart like that shown in Figure 2.16 would have been more appropriate. CHAPTER OUTCOME #5 Stem and Leaf Diagrams Another graphical technique that is useful for doing a preliminary analysis of quantitative data is called the stem and leaf diagram. The stem and leaf diagram is similar to the histogram introduced in Section 2-1 in that it displays the distribution for the quantitative variable. However, unlike the histogram, in which the individual values of the data are lost if the variable of interest is broken into classes, the stem and leaf diagram shows the individual data values. Minitab has a procedure for constructing stem and leaf diagrams. Although Excel does not have a stem and leaf procedure, the PHStat add-ins to Excel that are included on the CD-ROM do have a stem and leaf procedure. FIGURE 2.15 Pie Chart: Per Student Funding for Universities Lewis and Clark College, $5,410 Boise State University, $5,900 Idaho State University, $6,320 University of Idaho, $7,143
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Chapter 2: Graphs, Charts, and Tables--Describing Your Data

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