426 Statistical Methods
on the basis of the city variable and
then add trend lines to each of the four
cities. Include the four regression equa-
tions on the chart. Do the slopes appear
to be the same for the different cities?
g. Save your changes to the workbook
and write a report summarizing your
observations.- Continue to explore the data from the
Cola workbook discussed in this chapter
by performing the following analysis:
a. Open the Cola workbook from the
Chapter10 folder and save it as Cola
Oneway ANOVA.
b. Create boxplots and multiple histo-
grams of the foam variable for the dif-
ferent cola brands.
c. Because the two-way ANOVA per-
formed in the chapter showed that the
interaction term and the type effect
were not signfi cant, redo your analy-
sis as a one-way ANOVA with cola as
the single factor.
d. Create a matrix of paired differences,
using the Bonferroni correction.
Which pairs of colas are different in
terms of their foam volume?
e. Save your changes to the workbook and
write a report summarizing your results. - You’ve been given a workbook that con-
tains information on 32 colleges from
the 2008 edition of U.S. News and World
Report’s “America’s Best Colleges,”
which lists 248 national liberal arts col-
leges in four tiers. The fi rst two tiers are
combined in a list of 125 colleges, and
there are 61 in tier three and 62 in tier
four. Splitting the 125 into 62 and 63,
you have four tiers with 62, 63, 61, and
62 colleges, respectively. A random sam-
ple of eight was drawn from each of the
four tiers, excluding nonprivate colleges.
The data set includes Tier (from 1 to 4),
College, Expenses (including tuition and
fees but not room and board), and InState
(the percentage of students who come
from within the state). Perform the fol-
lowing analysis on the data set:
a. Open the Four Year workbook from
the Chapter10 folder and save it as
Four Year ANOVA.
b. Create a multiple histogram of the
tuition for different tier levels. Are there
apparent problems with the normality
and constant variance assumptions?
c. Perform a one-way ANOVA to com-
pare expenses in the four tiers. Does
the tier affect the cost of attending a
private college?
d. Create a matrix of paired mean differ-
ences. Does it cost signifi cantly more
to attend a college in a more presti-
gious tier?
e. Notice that the means for expenses
decrease roughly linearly as the tier
number increases. Accordingly, re-
gress Expenses on Tier. Interpret the
tier regression coeffi cient in terms of
the drop in expenses when you move
to a higher tier number. Conversely,
how much more does it cost to attend
a college in a more prestigious tier
(with a lower tier number)?
f. Save your changes to the workbook
and write a report summarizing your
results, stating whether it is more
expensive to attend a highly rated col-
lege and, if so, how the cost is related
to the rating. Compare the regression
and the ANOVA.- The Four Year workbook of Exercise 10
includes InState, the percentage of stu-
dents coming from within the state. How
does the InState variable depend on tier?
a. Open the Four Year workbook from
the Chapter10 data folder and save it
as Four Year Instate ANOVA.
b. Create a boxplot of InState broken
down by tier. Notice the outlier in
tier 4. Which college is it, and how