Statistics 101 – Homework 5
Due Monday, February 26, 2007
Homework is due on the due date at the end of the lecture.
Reading:
February 16
February 19 – February 23
Chapter 11
Chapters 12 & 13
Assignment:
1. Ipsos Public Affairs conducted a public opinion survey between February 5th and 7th,
2007. 1,000 randomly selected adults from across the United States were contacted and
asked the question, “Generally speaking, would you say things in this country are they
heading in the right direction, or are they off on the wrong track?” 28% of the people
contacted answered that things in this country are heading in the right direction, 68%
answered that things in this country were off on the wrong track, and 4% were unsure.
a) Identify the population.
b) Identify the population parameter of interest.
c) Identify the sample.
d) Identify the sampling method, including whether or not randomization was
employed.
e) Identify any potential sources of bias you can detect and any problems you see in
generalizing to the population of interest.
2. How popular is Facebook at ISU? Listed below are some ideas proposed for finding out
what proportion of students at ISU are registered on Facebook. For each, indicate what
kind of sampling strategy is involved and what (if any) biases might result.
a) Interview your friends and find out what proportion of them are registered on
Facebook.
b) Put an ad in the ISU Daily asking students to log into the Daily web site and
indicate whether or not they are registered on Facebook.
c) Select an apartment complex in Ames at random and contact every resident in the
apartment complex find out whether or not each is registered on Facebook.
d) Select a dorm on the ISU campus at random and contact every resident in the
dorm to find out whether or not each is registered on Facebook.
e) Randomly select 200 ISU students from the ISU directory and contact them by
phone to find out whether or not each is registered on Facebook.
f) Ask the Registrar to select every 200th student, starting with a randomly selected
student, on the list of all students enrolled at ISU and provide addresses, phone
numbers and emails so that those students selected can be contacted to find out
whether or not each is registered on Facebook.
3. Below is a list of 10 individuals, name and gender. We wish to select 3 individuals at
random from the list of 10.
0 Kaeli (F)
5 Kristi (F)
1 Ryan (M)
6 Dawn (F)
2 Lindsey (F)
7 Alisha (F)
3 Jon (M)
8 Juan (M)
4 Matt (M)
9 Amy (F)
a) Explain how you would use the table of random numbers in the back of your text
(row 14 starting from the left) to select a simple random sample of three
individuals. Who are the three individuals selected?
b) Describe how you would randomly sample to ensure that there would be one
male (M) and two females (F) chosen.
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4. The following is taken from an article in the Des Moines Register, January 14, 2007,
page 4AA entitled “Study: Milk blunts heart benefits of tea.”
“There are a lot of studies that show that tea is protective against cardiac diseases,” said
lead researcher Dr. Verena Stangl, professor of cardiology at the Charite Hospital,
Universitatsmedizin-Berlin, in Germany.
“If you look at the studies, you see that in Asia there are less cardiac diseases, but in
England that’s not the case. So the question is, is the addition of milk a reason for this
difference between Asia and England, where tea is often taken with milk?” she said.
In the study, 16 healthy postmenopausal women drank either half a liter of freshly
brewed black tea, black tea with 10 percent skimmed milk, or boiled water on three
different occasions. The researchers then measured the function of the cells lining the
brachial artery in the forearm before and two hours after beverage consumption.
Stangl’s team found that black tea significantly improved the ability of the arteries to
relax and expand. “But when we added milk, we found the biological effect of teas was
completely abolished,” she said.
a)
b)
c)
d)
e)
f)
Why is this study an experiment?
What is the response variable?
What is the explanatory variable?
What treatments are compared?
Is there a placebo? Explain briefly.
Is this a “blind” study, e.g. are participants not aware of which treatment group they
are in? Explain briefly.
g) What important information about the design of the study does not appear in the
article?
h) Based on a combination of the information in the article and your knowledge of sound
study design, make a diagram that shows how you think the study was designed.
Hint: Look at pages 292-293 in the text
5. The following is taken from an article in the Des Moines Register, January 14, 2007,
page 4AA entitled “Kidney disease linked to blood flow problems.”
People with chronic kidney disease have an increased risk of peripheral arterial disease
(PAD), a condition that causes reduced blood flow in the legs and can lead to amputation.
In the study more than 14,000 middle age adults were enrolled and followed for an
average of 13 years. The participants were split into three groups: those with normal
kidney function; those with mildly decreased kidney function; and those with late stage
chronic kidney disease. After adjusting for age, race, and sex, the study authors found
the rate of PAD was nearly two times higher in chronic kidney disease participants than
in people with normal kidney function.
a)
b)
c)
d)
e)
Why is this an observational study and not an experiment?
Is it a retrospective or prospective study? Explain briefly.
Who are the subjects studied?
What is the explanatory variable? What is the response variable?
Does this study prove that chronic kidney disease causes peripheral arterial disease?
Explain briefly.
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