ASSIGNMENT 3: CHAPTER 3 (30 points)
All problems taken from Introduction to the Practice of Statistics, Fifth
Edition by David S. Moore and George P. McCabe.
3.3 (3 points) One study of cell phones and the risk of brain cancer looked
at a group of 469 people who have brain cancer. The investigators matched
each cancer patient with a person of the same sex, age, and race who did
not have brain cancer, then asked about use of cell phones. Result: “Our
data suggest that use of handheld cellular telephones is not associated with
risk of brain cancer.” Is this an observational study or an experiment?
Why? What are the explanatory and response variables?
3.5 (3 points) An educational software company wants to compare the
effectiveness of its computer animation for teaching cell biology with that of
a textbook presentation. The company tests the biological knowledge of
each of a group of first-year college students, then divides them into two
groups. One group uses the animation, and the other studies the text. The
company retests all the students and compares the increase in
understanding of cell biology in the two groups. Is this an experiment? Why
or why not? What are the explanatory and response variables?
3.10 (4 points) Most American adolescents don’t eat well and don’t
exercise enough. Can middle schools increase physical activity among their
students? Can they persuade students to eat better? Investigators
designed a “physical activity intervention” to increase activity in physical
education classes and during leisure periods throughout the school day.
They also designed a “nutrition intervention” that improved school lunches
and offered ideas for healthy home-packed lunches. Each participating
school was randomly assigned to one of the interventions, both
interventions, or no intervention. The investigators observed physical
activity and lunchtime consumption of fat. Identify the experimental units or
subjects, the factors, the treatments, and the response variables.
3.12 (6 points) The Bayer Aspirin Web site claims that “Nearly five
decades of research now link aspirin to the prevention of stroke and heart
attacks.” The most important evidence for this claim comes from the
Physicians’ Health Study, a large medical experiment involving 22,000 male
physicians. One group of about 11,000 physicians took an aspirin every
second day, while the rest took a placebo. After several years the study
found that subjects in the aspirin group had significantly fewer heart attacks
than subjects in the placebo group.
(a) (3 points) Identify the experimental subjects, the factor and its levels,
and the response variable in the Physicians’ Health Study.
(b) (2 points) Use a diagram to outline a completely randomized design for
the Physicians’ Health Study.
(c) (1 point) What does it mean to say that the aspirin group had
“significantly fewer heart attacks”?
3.38 (6 points) For each of the following sampling situations, identify the
population as exactly as possible. That is, say what kind of individuals the
population consists of and say exactly which individuals fall in the
population. If the information given is not complete, complete the
description of the population in a reasonable way.
(a) (2 points) An opinion poll contacts 1161 adults and asks them, “Which
political party do you think has better ideas for leading the country in the
(b) (2 points) A furniture maker buys hardwood in large lots. The supplier
is supposed to dry the wood before shipping—wood that is not dry won’t
hold its size and shape. The furniture maker chooses 5 pieces of wood from
each lot and tests their moisture content. If any piece exceeds 12%
moisture content, the entire lot is sent back.
(c) (2 points) The American Community Survey (ACS) will replace the
census “long form” starting with the 2010 census. The main part of the ACS
contacts 250,000 addresses by mail each month, with follow-up by phone
and in person if there is no response. Each household answers questions
about their housing, economic, and social status.
3.56 (4 points) The Excite Poll can be found online at poll.excite.com. The
question appears on the screen, and you simply click buttons to vote “Yes,”
“No,” “Not sure,” or “Don’t care.” On February 17, 2004, the question was
“Do you think that beer advertisements are targeted towards minors?” In
all, 4316 (29%) said “Yes,” another 8986 said “No,” and the remaining 1182
were not sure or didn’t care.
(a) (2 points) What is the sample size for this poll?
(b) (2 points) That’s a much larger sample than standard sample surveys.
In spite of this, we can’t trust the result to give good information about any
clearly defined population. Why?
State whether each boldface number in Exercises 3.62 to 3.65 is a
parameter or a statistic.
3.62 (2 points) An opinion poll uses random digit dialing equipment to dial
2000 randomly chosen residential telephone numbers. Of these, 621 are
unlisted numbers. This isn’t surprising, because 35% of all residential
numbers are unlisted.
3.64 (2 points) The Tennessee STAR experiment randomly assigned
children to regular or small classes during their first four years of school.
When these children reached high school, 40.2% of blacks from small
classes took the ACT or SAT college entrance exams. Only 31.7% of blacks
from regular classes took one of these exams.