Lesson 6.2.1
6-46. Here are some more news headlines from real observational studies. Just as you did in problem 6-43,
determine at least one plausible lurking variable that could explain the cause and effect. Remember, do not argue
about the link expressed in the headline. Accept the association or link as true. Your task is to find the other
variable(s) that could be the actual cause(s).
a. “Teens with own cars more likely to crash”
[ With a car readily available these teens might simply be driving more and the extra time on
the road is causing them to be in more crashes. ]
b. “Study connects hyperactivity, food additives”
[ A child who eats more than average amounts of food additives may have parents who have a
relaxed attitude about meals, schedules and overall discipline this may cause a child to appear
hyperactive at school. ]
c. “The graveyard shift may be aptly named. Working nights will soon be listed as a likely cancer cause”
[ Many nighttime jobs involve working in bars, casinos, or restaurants where smoking is
prevalent. Night employment is generally considered less desirable so people who work at
night may have less money and therefore less access to medical care. ]
d. “Daily meat diet tied to higher chance of early death”
[ This might be connected to gender. Men as a group eat more meat and don’t live as long as
women. Also, if the meat is highly processed like hotdogs, it might be the additives that are
harmful and not the meat itself. ]
6-47. Explain the difference between an association and causation. How could a researcher prove causation?
[ Association means that two or more things are related. Causation is when one event actually
leads to another.]
Lesson 6.2.2
6-54. Consider the question: “Does a traditional classroom SAT preparation course improve scores more than an
on-line study course?” Design an experiment that could help to answer this question. Refer to problem 6-48
for ideas. [ See sample diagram below. ]
6-55. Design experiments for the following statistical questions. If it would be unethical to conduct such an
experiment, state why.
a. “Does listening to classical music during a math test improve scores?”
[ The simplest way to set up this study would be to get a large group of volunteers and
randomly assign them to two groups who will take the same math test in different rooms. In
one room classical music is played and no music is played in the other (control group). The
scores from the groups could be averaged and compared. An expanded version of the
experiment could have additional groups listening to other kinds of music while taking the test
for comparison. ]
b. “Do seat belts save lives in car crashes?”
[ People would need to be randomly assigned to random cars that will crash. One group would wear
seatbelts the other would not and the percentage of fatalities would be measured and compared.
Clearly this is not ethical but reasonable results might be obtained in an experiment using crash
dummies instead of human subjects. ]
c. “Does vitamin C help prevent colds?”
[ A large group of volunteers would be randomly selected and exposed to a cold virus. The
subjects would be randomly assigned to two treatment groups. One group gets a daily vitamin
C supplement and the other group receives a daily placebo. The percentage of each group that
contracts a cold could be calculated and compared. ]
Lesson 6.2.3
6-57. Answer some of the same questions from these actual newspaper headlines. If an observational study was
done, explain how. Explain why an experiment was not possible. If the study shows an association between
variables, discuss the effects of at least two possible lurking variables. If you believe an experiment was done, state
so, and outline a possible experimental design. If surveys were necessary, list a potential source of bias in the
question(s), and a potential difficulty in getting a representative sample from the population.
a. “Study sticks it to traditional back care. Acupuncture – real and fake – gets better results for pain than
the usual treatments.”
[ Because a placebo is mentioned this most certainly was an experiment. A group of volunteers
with back pain were randomly distributed between at least 3 test groups. One group received
traditional medical care, another got acupuncture treatments and the last got fake
acupuncture. The difference in pain reported by each patient was likely averaged for each
group and the averages compared. Measuring the subjects’ pain was likely done by survey, i.e.,
“Rate your back pain today from 1 to 10…” The physical surroundings of the interview or the
compassion level of the interviewer may be a source of bias. ]
b. “MARITAL STRIFE A HEART WRECKER? Bad marriage can risk coronary disease risk, researchers say”
[ This is an observational study. A large group of people were given questionnaires including
questions about their marriage and their health. This cannot be an experiment because a
randomly selected group of people would have to be forced into “bad” marriages and their
cardio health compared to a group forced into “not bad” marriages. Perhaps people under a
great deal of stress tend to have bad marriages and tend to have heart problems. Maybe
people with addiction problems tend to have bad marriages and tend to have heart problems.
Surveys were used. Trying to get a random sample of responses from the world’s married
population would be nearly impossible. It is likely the respondents had something in common
like an employer or health plan. Maybe having a bad marriage or heart condition made people
more likely to respond to the survey. What constitutes a “bad” marriage? Questions that start
with “Have you ever …” could bias the results, e.g. … thought about a divorce … had a
disagreement with your spouse … etc. ]
c. “Breastfeeding May Cut Breast Cancer Risk. Women with a family history of breast cancer who have
ever breastfed reduce their risk of getting premenopausal breast cancer by nearly 60%, according to a
new study.”
[ This is an observational study. A large group of women were given questionnaires including
questions about breastfeeding and whether they have had breast cancer. This cannot be an
experiment because a randomly selected group of women would have to be forced to
breastfeed their children and their breast cancer rates compared to another group forced to
not breastfeed their children. Perhaps the kind of woman who breast feeds her child is less
likely to drink alcohol or smoke. Maybe women who breast feed eat healthier foods than those
who do not. Surveys were used. Trying to get a random sample of responses from the world’s
population of women with a family history of breast cancer would be nearly impossible. It is
likely the respondents had something in common like an employer or health plan. Maybe the
type of person who takes (or has) the time to breast feed their children, also takes the time to
fill out health surveys, so that group was over represented in the sample. ]
d. “Study: Oral drug better than lotion to kill lice… A new study has found that in tough cases, an (new)
oral medication kills the parasites more effectively than a prescription lotion applied to the scalp.”
[ The word “study” is used in the headline but because the oral medication is new, an
observational study is not possible. This is an experiment. As an experiment it required a
number of volunteers already infected with head lice. They need to be randomly assigned to at
least two groups, three if a placebo medication is included. One group gets the oral medication
and the other gets the prescription lotion. After a period of time the number of lice on each
person is counted and the group averages compared. ]