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Chapter 1
1. (Hypothetical) A researcher wants to determine the effectiveness of a high blood
pressure medicine. She takes a random sample of 1,000 people and finds that 328 have
been diagnosed with high blood pressure. She makes these 328 into the treatment group
and assigns the remainder to the control group. She then administers the medicine to the
treatment group. Is this an effective test of the medicine? Why or why not?
2. (Hypothetical) In an effort to improve English grades, the principal of a high school
coordinates a special after-hours study session. To populate the session, he randomly
chooses 15 students from each English class. After one semester, he compares the
number of A’s for his special students with the number of A’s for everyone else. The
results were as follows:
Special Group
Regular Students
Total
60
240
A’s in English
17
61
Percent Rate
28.3%
25.4%
a) Was this controlled study double-blind? Why or why not?
b) Does this data support a significant link between attending the sessions and higher
English grades? Why or why not?
c) Give at least one possible confounding factor in this study.
3. Explain why, in general, researchers use placebos in the control group.
4. (AP) In 1998, a study was done to see if antiperspirant was effective at slowing the
development of blisters. Cadets from the US Military Academy were divided into two
groups. For three nights before a 13-mile hike, one group used antiperspirant on their
feet while the other used a placebo. After the hike, the researchers reported that 21
percent from the antiperspirant group reported blisters, as opposed to 48 percent from the
placebo group. Does antiperspirant seem effective at retarding the occurrence of blisters?
5. (Hypothetical) A psychologist wants to show that people become more stressed
without knowing what time it is. He takes 80 volunteers from a college, asks them not to
bring any timepieces, and divides them equally into groups. Each volunteer is placed,
one at a time, in an office and asked to wait for the psychologist to come in. For
members of the first group, there was no clock in the room; a clock was placed in the
room for members from the second group. After 60 minutes of waiting, the psychologist
came in and asked the subjects to rate their stress levels from a scale of 1 (not stressed) to
10 (very stressed).
a) Was this study randomized controlled?
b) Was this a double-blind study?
6. (Hypothetical) A pharmaceutical company wants to show that its new drug is effective
at treating the common cold. It obtains 200 volunteers with colds and divides them into
equally sized treatment and control groups, giving the control group a placebo. The
company then checks the following day to see how many people from each group no
longer have cold symptoms.
a) Why did the company screen out people without colds?
b) Was this a double-blind study?
c) Give at least one possible confounding factor in the study.
7. (AP) In 2002, the results of a study indicating that a drug used to quit smoking and
treat depression were published. For the study, 227 obese people were randomly
assigned into three groups; one group got two daily doses of the drug, one group got one
dose, and the third group got a placebo. The participants also were placed on a restricted
diet and asked to increase their exercise by about 50 percent.
Over the next 24 weeks, 35 of the participants dropped out of the program. Of the
remainder, those on the higher dosage lost 10 percent of their body weight compared with
7 percent for those on the lower dosage. Those who took the dummy pill lost about 5
percent of their body weight.
a) Does the drug seem to cause weight loss among obese people?
b) Give at least one possible confounding factor in this study.
8. (Hypothetical) A TV commercial observes that volunteers who switched to having to
Cheerios for breakfast reduced their cholesterol level by 4%.
a) Is this referencing a controlled experiment?
b) Does this show that Cheerios cereal is effective in reducing your cholesterol level?
Why or why not?
9. (ABC news) A study done in 2001 claims that taking palmetto pills is an effective
treatment for men with lower urinary tract symptoms associated with a large prostate.
The study examined the effects of saw palmetto in 85 men over the course of six months.
Patients taking the plant supplement were compared to patients taking placebos. The
study found that the men taking saw palmetto reported a greater improvement in
symptoms compared to those taking the placebo.
a) How should the subjects have been divided to minimize bias?
b) Did the palmetto pills cause reduced urinary tract symptoms for men with enlarged
prostates?
10. (Washington Post) In 2003, the results of a study exploring the effects of the hormone
progesterone on premature births were published. Out of 459 women who had previously
given birth prematurely (the biggest indication of risk for more premature births), 306
were given weekly injections of progesterone. The other 153 women were injected with
a placebo. The treatment group’s chance of premature births was reduced by 34 percent.
The study was carried out at the 19 centers that make up the Maternal-Fetal Medicine
Units Network.
a) Did progesterone reduce the risk of premature birth? Why or why not?
b) Which, if any, confounding factors considered?