56 Chapter 2 Describing and Exploring Data
Exercises
Many of the following exercises can be solved using either computer software or pencil and
paper. The choice is up to you or your instructor. Any software package should be able to work
these problems. Some of the exercises refer to a large data set named ADD.dat that is available at
http://www.uvm.edu/~dhowell/methods7/DataFiles/Add.dat. These data come from an actual research
study (Howell & Huessy, 1985). The study is described in Appendix: Data Set on page 692.
2.1 Any of you who have listened to children tell stories will recognize that children differ from
adults in that they tend to recall stories as a sequence of actions rather than as an overall
plot. Their descriptions of a movie are filled with the phrase “and then... .” An experi-
menter with supreme patience asked 50 children to tell her about a given movie. Among
other variables, she counted the number of “and then.. .” statements, which is the depend-
ent variable. The data follow:
18 15 22 19 18 17 18 20 17 12 16 16 17 21 23 18 20 21 20 20 15 18 17 19 20
23 22 10 17 19 19 21 20 18 18 24 11 19 31 16 17 15 19 20 18 18 40 18 19 16
a. Plot an ungrouped frequency distribution for these data.
b. What is the general shape of the distribution?
2.2 Create a histogram for the data in Exercise 2.1 using a reasonable number of intervals.
2.3 What difficulty would you encounter in making a stem-and-leaf display of the data in
Exercise 2.1?
2.4 As part of the study described in Exercise 2.1, the experimenter obtained the same kind of
data for 50 adults. The data follow:
10 12 5 8 13 10 12 8 7 11 11 10 9 9 11 15 12 17 14 10 9 8 15 16 10
14 7 16 9 1 4 11 12 7 9 10 3 11 14 8 12 5 10 9 7 11 14 10 15 9
a. What can you tell just by looking at these numbers? Do children and adults seem to re-
call stories in the same way?
b. Plot an ungrouped frequency distribution for these data using the same scale on the axes
as you used for the children’s data in Exercise 2.1.
c. Overlay the frequency distribution from part (b) on the one from Exercise 2.1.
2.5 Use a back-to-back stem-and-leaf display (see Figure 2.6) to compare the data from Exer-
cises 2.1 and 2.4.
2.6 Create a positively skewed set of data and plot it.
2.7 Create a bimodal set of data that represents some actual phenomenon and plot it.
2.8 In my undergraduate research methods course, women generally do a bit better than men.
One year I had the grades shown in the following boxplots. What might you conclude from
these boxplots?
0.950.850.751
1 = Male, 2 = Female20.65PercentSex