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

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