Chapter 6 Statistical Inference 271
e. Redo your analysis using the Wil-
coxon Signed Rank test. How do
your results compare to the paired
t test?
f. Redo questions b through e using the
refusal rates for high-income whites
and minorities. How do the results of
the two analyses compare, especially
in terms of the confi dence interval
for the difference in refusal rate? Is
there evidence to suggest that there is
no refusal rate gap for higher-income
minorities?
g. Save your changes to the workbook
and write a report summarizing your
conclusions.
- The Teacher.xls workbook stores average
teacher salary, public school spending
per pupil, and the ratio of teacher to
pupil spending for 1985, broken down
by state and region. Analyze the results
stored in this workbook.
a. Open the Teacher workbook from
the Chapter06 folder and save it as
Teacher Analysis.
b. Construct a 95% t confi dence interval
for each of the numeric variables, bro-
ken down by area.
c. Construct a 95% Wilcoxon Signed
Rank confi dence interval for the nu-
meric variables, by area.
d. Save the changes to your workbook
and write a report summarizing the
results of your analysis.
- The Pollution workbook contains data
on the number of unhealthful pollution
days for 14 U.S. cities comparing 1980
values to average values from 2000 to
2006. Analyze what impact environmen-
tal regulations have had on pollution.
a. Open the Pollution workbook from
the Chapter06 folder and save it as
Pollution Analysis.
b. State your null and alternative
hypotheses for this analysis.
c. Create histograms of the ratio and
difference between the 1980 and 2006
values. Does the distribution of those
two variables appear to follow the
normal distribution?
d. Analyze the difference and ratio
values using a one-sample t test,
s test, and a Wilcoxon Signed Rank
test.
e. Save your changes to the workbook.
Write a report summarizing your
observations. Where do you see sig-
nifi cant changes in the number of
pollution days? Is this true for all sta-
tistical tests? Given the distribution of
the data, which test appears to be the
most appropriate for these values?
- In a NASA-funded study, seven men and
eight women spent 24 days in seclusion
to study the effects of gravity on circula-
tion. Without gravity, there is a loss of
blood from the legs to the upper part of
the body. The study started with a nine-
day control period in which the subjects
were allowed to walk around. Then
followed a ten-day bed-rest period in
which the subjects’ feet were somewhat
elevated to simulate weightlessness in
space. The study ended with a fi ve-day
recovery period in which the subjects
again were allowed to walk around.
Every few days, the researchers mea-
sured the electrical resistance at the calf,
which increases when there is a blood
loss. The electrical resistance gives an
indirect measure of the blood loss and
indicates how the subject’s body re-
sponds to the conditions. You’ve been
asked to examine whether the male sub-
jects and the female subjects differed in
how they responded to the study. You’re
to perform your analysis for each of the
days in the study.
a. Open the Space workbook from the
Chapter06 folder and save it as Space
Biology Analysis.
