Name ________________________________Date____________________Period________
Review Sheet for Test on Unit 6: Experiments
Statistics
1. A drug company wants to test a new nasal spray that they think will help prevent the
common cold. A group of 300 volunteers is available for the study. Half will be assigned the
new nasal spray and the other half will receive a placebo. At the end of the normal “fluseason” the proportion of those who received the new nasal spray and got the flu will be
compared to the proportion of those who received the placebo and got the flu.
(a) Identify the explanatory variable and the response variable for this study.
Explanatory: used the nasal spray or didn’t; response: got the flu or didn’t get the flu.
(b) Explain the meaning of the word “placebo” in the above description. Then discuss why it
was important to administer a placebo as part of the design of this experiment.
The placebo is a spray that looks, smells, and is packaged the same as the real spray but
contains no active ingredients. A placebo is necessary for several reasons. It is important
to administer a placebo to quantify the placebo effect: how much subjects improve from
taking any treatment they think might be beneficial. The placebo group provides a
baseline for comparison with the drug treatment group. This allows us to see whether the
rate of flu prevention is higher for the nasal spray than it is for the placebo, since some
people respond favorably to any treatment if even if it contains inert ingredients.
(c) Describe carefully how you would randomly assign the 300 volunteers to the two nasal
sprays.
Randomly allocate the subjects into two groups of 150. Use the random digit chart. Have
subjects in the first group take the nasal spray daily. The subjects in the second group
should use the placebo spray daily.
2.
In a study of stress, three different methods (walk 60 minutes per day, one hour of yoga,
and 45 minutes of meditation) will be tried on a randomly selected group of adults who
work at a large company to see which method is most effective in reducing stress. A
measure of stress will be done before the experiment begins and another six months later
at the end of the study.
(a) Can this study be blinded? Explain.
The subjects cannot be blinded since they are being told to walk, do yoga or meditate. The
evaluators of the results, however, should be blinded.
(b) Should the study be blocked? Explain.
It doesn’t appear necessary to block this study as you are trying to evaluate which of the three
methods would be effective in reducing stress. Since it is a large company, there may be
certain departments where there is more stress than in others. If a student indicates a
plausible blocking variable, they should explain why they think this would affect the stress of
the employees.
(c) Would a control group be necessary? Explain.
A control group would be helpful in this situation. It provides baseline data that would tell us
whether any of the three methods actually works at all.
(d) What advantage would a control group provide?
Many things can happen over a six-month period. Suppose the company is competing for a
very large contract and failing to get the contract would have dire financial consequences
for the company. Half-way through the six months, the company is awarded the contract.
There might be a lowering of stress levels not due to any of the particular treatments but
due to the financial survival of the company. A control group would give us a measure of
that reduction which we can then compare to any reduction achieved by the three
treatments.
(e) Describe an appropriate design including how to randomize the subjects.
Any of the methods previously described in Quiz 6.1A, answer 2b are acceptable. Since no
numbers are given in the problem, a student can make up their own size to randomly
assign to the four groups. For example, 120 employees assigned to four groups of 30.
3. You are participating in the design of a medical experiment to investigate whether a new
dietary supplement will reduce the cholesterol level of middle-aged men. Sixty randomly
selected men are available for the study. It is know from past studies that smoking and
weight can affect cholesterol levels in men.
(a) Can this experiment be blinded?
.
Yes, blinding of both subjects and evaluators can be done.
(b) Identify the explanatory and response variable.
Explanatory variable: whether or not the subject receives a dietary supplement; Response
variable: measure of cholesterol level.
(c) Explain how blocking could be used to take smoking into account in this experiment.
Make sure to describe your blocking criteria and how you will randomize subjects.
If we think that smoking is most closely associated with cholesterol, we would divide
the subjects by whether or not they smoked. Suppose that you end up with 20 smokers.
Put their names in a hat and draw out 10 names. These will be assigned to the dietary
supplement. The remainder will be assigned to the placebo. Do the same with the 40
nonsmokers with 20 per group.
(d) Explain how blocking could be used to take weight into account in this experiment. Make
sure to describe your blocking criteria and how you will randomize subjects.
If you think that weight is most closely associated with cholesterol levels, then block on
weight. Pair the two men closest in weight in each block – the two heaviest, the next
two heaviest, down to the two who weigh the least.
4. Students at a large high school are curious about the effects of peer pressure. They
wonder whether students are more likely to wash their hands after using the bathroom
when others are present. The students decide to carry out an experiment in the school’s
restrooms during lunch. A student researcher hides in one of the stalls in each restroom.
This student’s task is to observe whether each subject washes his/her hands after using
the bathroom.
As each student enters the bathroom, a second student researcher stationed outside flips a
coin. If the coin shows heads, this researcher will enter the restroom and pretend to clean a
pair of sunglasses. If the coin shows tails, this researcher will remain outside. At the end of
the experiment, the researchers can simply compare how often students washed their hands –
when they were in the presence of others versus when they thought they were alone.
a. State the three basic standards of data ethics that should be met in any experiment, and explain
the purpose of each one in a sentence or two.
The three basic principles of data ethics are: getting the study approved by an Institutional
Review Board, obtaining informed consent, and ensuring confidentiality of individual data. It
is the Institutional Review Board’s primary job to ensure the safety of the subjects in the
experiment. Experimenters owe it to prospective subjects to disclose potential risks to subjects
before obtaining their consent to participate. Subjects should be able to expect that their
privacy will not be violated, such as by releasing personal information obtained in an
experiment.
b. Discuss two reasons that you believe this experiment is not ethical.
There is no attempt to obtain informed consent from potential subjects. Subjects are being
“spied on” without their knowledge in a private setting (bathroom). There is tremendous
potential for embarrassment if confidentiality is violated since the researchers might very w ell
know some of the unsuspecting “subjects.”
Use the random digits table from the book.
5. A nutritionist is interested in whether excessive sugar intake causes hyperactivity in children.
Two different study designs are contemplated to examine this issue.
Design I: One hundred children with their parents’ permission are to be subjects in the study.
The nutritionist will randomly divide the children into two groups of fifty. Both groups
of children will eat similar diets for a week including a bowl of cereal, a sandwich, a
main course, four glasses of a special milkshake, and two candy bars per day.
However, in preparing the food in one of the groups' diets, all of the sugar is to be
replaced with an artificial sweetener (so the children cannot tell the difference between
the two diets). A psychologist who does not know which diet the children were on will
then watch them at play and classify each child as showing signs of hyperactivity or as
showing no signs of hyperactivity.
Design II: One hundred children will be watched while they play by a psychologist who will
classify each child as showing signs of hyperactivity or as showing no signs of
hyperactivity. This data will then be compared with the results of a diet questionnaire
filled out by the children’s parents which gives information about the children’s sugar
intake over the previous week.
Compare and contrast these two studies. Cite at least one similarity and one difference.
The biggest difference is that Design I is a completely randomized experiment and Design II is
an observational study. Another difference is that Design I is carried out in a double-blind
manner where neither the children nor the psychologists who are rating their activity levels
know who is receiving the artificial sweetener whereas observational studies such as Design
II, never are blinded. Both studies are similar in that they are attempting to determine the
relationship between sugar intake and activity level of children. Both designs similarly will
pose difficulties for researchers. Design I will be difficult to carry out due to the simple
logistics of preparing the lunches. Design II may provide evidence of an association between
sugar intake and hyperactivity, but because it is an observational study, causation cannot be
inferred.
The next three questions concern this situation: Does using a cell phone while driving make an
accident more likely? Researchers compared telephone company and police records to find 699
people who had cell phones and were also involved in an auto accident. Using phone billing
records, they compared the frequency of accidents when cell phones were in use to the frequency
when they were not in use.
1. This study is
(a) a randomized comparative experiment.
(b) an experiment, but without randomization.
(c) a simple random sample.
(d) an observational study, but not a simple random sample.
(e) none of the above
2. The explanatory variable in this study is
(a) whether or not the subject had an auto accident.
(b) whether or not the subject was using a cell phone.
(c) the risk of an accident.
(d) whether or not the subject owned a cell phone.
(e) billing records.
3. An example of a lurking variable that might affect the results of this study is:
(a) whether or not the subject had an auto accident.
(b) whether or not the subject was using a cell phone.
(c) whether or not the subject was talking to a passenger in the car.
(d) whether or not the subject owned a cell phone.
(e) both (c) and (d).
4. Confounding often defeats attempts to show that one variable causes changes in another
variable. Confounding means that
(a) this was an observational study, so cause and effect conclusions are not possible
(b) the effects of several variables are mixed up, so we cannot say which is causing the
response
(c) we don't know which is the response variable and which is the explanatory variable
(d) we would get widely varied results if we repeated the study many times
(e) no randomization was used in the study.
Here is a shortened version of the summary of a paper in the New England Journal of Medicine
that compares the fate of heart attack victims in three types of hospitals. ("Acute myocardial
infarction" is medical jargon for a heart attack.) The next four questions concern this summary.
Background. "America's Best Hospitals," published annually by U.S. News & World Report, assesses the
quality of hospitals. It is not known whether patients admitted to hospitals ranked at the top in cardiology
have lower short term mortality from acute myocardial infarction than those admitted to other hospitals.
Methods. Using data from the Cooperative Cardiovascular Project on 149,177 elderly Medicare
beneficiaries with acute myocardial infarction in 1994 or 1995, we examined the care and outcomes of
patients admitted to three types of hospitals: those ranked high in cardiology (top ranked hospitals);
hospitals not in the top rank that had onsite facilities for cardiac catheterization, coronary angioplasty, and
bypass surgery (similarly equipped hospitals); and the remaining hospitals (non-similarly equipped
hospitals). We compared 30-day mortality . . .
Results. Admission to a top ranked hospital was associated with lower adjusted 30-day mortality (odds
ratio, 0.87; 95 percent confidence interval, 0.76 to 1.00).
5. The design of this study is
(a) a completely randomized experiment
(b) a randomized block experiment
(c) a multistage national sample survey
(d) a stratified national sample survey
(e) an observational study that compares several treatments
6. The explanatory and response variables are:
(a) explanatory = elderly Medicare beneficiaries; response = 30-day mortality
(b) explanatory = type of hospital; response = 30-day mortality
(c) explanatory = 30-day mortality; response = type of hospital
(d) explanatory = type of hospital; response = heart attack or not
(e) explanatory = 30-day mortality; response = elderly Medicare beneficiaries
7. The "odds ratio" compares two death rates. So the finding "odds ratio 0.87" means that on the
average the chance of dying at a highly ranked hospital is only 87% as great as at other hospitals.
The summary then gives a confidence statement about this odds ratio. "95 percent confidence"
means that
(a) the interval 0.76 to 1.00 came from a method that catches the true ratio in 95% of all
samples
(b) 95% of all the hospitals had a mortality rate between 0.76 and 1.00
(c) the mortality rate at highly ranked hospitals varies between 76% and 100% of the rate at other
hospitals
(d) we can be between 76% and 100% confident that the study results are correct
(e) many studies of this type have been undertaken, and in 95% of them, the odds ratio was
between 0.76 and 1.00.
8. The population about which the study draws conclusions is
(a) all adult residents of the U.S.
(b) all heart attack victims.
(c) elderly Medicare beneficiaries who are heart attack victims.
(d) doctors 40 years old or older.
(e) hospitals of all three types.
9. A study of the effect of government job training programs finds that the pay of workers after
training is higher than it was before training. A critic points out that workers often enroll for
training when their pay has recently dipped. So the effect of training in raising pay is mixed up
with the fact that pay would often rise when we measure from a low point. The statistical term
for this effect is
(a) confounding
(b) control
(c) nonresponse
(d) stratification
(e) common response
10. The most important advantage of experiments over observational studies is
(a) a well designed experiment can give good evidence that the treatments actually cause
the response.
(b) an experiment can compare two or more groups.
(c) we can use randomization to avoid bias in designing an experiment.
(d) we can study the relationship between two or more explanatory variables.
(e) we can gather data on a large group of subjects.
11. A psychologist is interested in the effects of religious conversion on alcoholics. She locates
50 alcoholics who have recently joined evangelical churches, and matches each with another
alcoholic of the same age, occupation and family status who has not joined a church. All 100
subjects are then observed for 5 years. This is
(a) an randomized comparative experiment.
(b) an experiment, but without randomization.
(c) a sample survey with randomly selected respondents.
(d) a comparative observational study.
(e) a randomized matched-pairs experiment.
12. Ethical standards for randomized, controlled clinical trials include
(a) not asking subjects to agree to participate without first informing them of the nature of
the study and possible risks and benefits.
(b) insuring that each subject knows which treatment he or she received.
(c) allowing subjects to decide whether or not to be in the control group
(d) never testing drugs which have not been proven to be completely safe.
(e) All of the above.
13. It was difficult to establish the causal link between cigarette smoking and lung cancer
because
(a) random allocation of subjects to smoking is unethical.
(b) observational studies generally cannot rule out confounding.
(c) those who choose to smoke may be genetically at greater risk for lung cancer than those who
don't choose to smoke.
(d) experiments done on animals may not be valid for humans.
(e) All of the above
The next two questions concern a newspaper article headlined, "Marrying young can be
beneficial." The article said:
Marriage is a good thing when it comes to cutting back on drinking and drugs. A University of
Michigan Institute for Social Research study of 33,000 young adults showed that young,
unmarried adults usually increased their alcohol, marijuana and cocaine use when they left home,
often to attend college. Those same people, however, decreased their drug and alcohol use when
they got engaged or married. Couples who lived together but were not engaged or married
showed no such drop in drug use.
14. The strongest reason for having reservations about the claim made in the first sentence of the
quote is
(a) don't agree with the claim.
(b) the sample size is too small.
(c) the study was limited to Michigan.
(d) there is no control group.
(e) it's an observational study.
15. The explanatory variable in this study is
(a) the level of alcohol, marijuana and cocaine use.
(b) marital status.
(c) year in college (e.g., freshman, sophomore, etc.).
(d) not given in the quote above.
(e) There is no explanatory variable because this is an observational study.
16. You want to ask a sample of undergraduates at State Tech how they feel about a proposal to
delay future Spring Breaks by a week. Opinions may differ depending on the class of the student,
especially because seniors will have left before the policy is changed. So you take separate SRS's
of seniors and non-seniors and combine them to form your sample. You used a
(a) simple random sample.
(b) stratified random sample.
(c) multistage sample.
(d) completely randomized experiment.
(e) randomized block experiment.
17. You work for an advertising agency that is preparing a new television commercial to appeal
to women. You have been asked to design an experiment to compare the effectiveness of three
versions of the commercial. Each subject will be shown one of the three versions and then asked
her attitude toward the product. You think there may be large differences between women who
are employed and those who are not. Because of these differences, you should use
(a) a completely randomized design.
(b) a categorical variable.
(c) a block design.
(d) a matched pairs design.
(e) a multistage sample.
Does taking large amounts of vitamins protect against cancer? To study this question, researchers
enrolled 29,000 Finnish men, all smokers over the age of 50. Half of the men took vitamin
supplements, and others took a dummy pill that has no active ingredient. The researchers
followed all the men for eight years. At the end of the study, men in the vitamin group were no
less likely to have cancer than men in the other group. This study cast doubt on the popular idea
that taking lots of vitamins can reduce the risk of cancer. The next six questions are based on
this study. The study design looked like this:
18. The statistical name for this study design is
(a) simple random sample.
(b) stratified random sample.
(c) randomized comparative experiment.
(d) multistage sample.
(e) observational study.
19. The method used to form the groups should appear in the outline at the point marked
(Question A). What is this method?
(a) Random allocation.
(b) Voluntary response.
(c) First come, first served.
(d) The double-blind method.
(e) Stratified sampling.
20. Treatment 2 was a dummy pill. Such a dummy treatment is called a
(a) double blind.
(b) categorical variable.
(c) nonsampling error.
(d) placebo.
(e) comparative.
21. The response variable should be named in the outline at (Question C). The response variable
in this study is
(a) whether or not a subject took vitamins.
(b) 29,000 Finnish men.
(c) random allocation.
(d) a confidence statement.
(e) whether or not a subject developed cancer.
22. In order to avoid unconscious bias, neither the subjects not the doctors who examined them
knew whether a particular subject was taking vitamins or dummy pills. This is called
(a) the placebo effect.
(b) the double-blind technique.
(c) the retrospective method.
(d) stratified sampling.
(e) internal validity.
23. A weakness of this study is that
(a) it isn't clear that the results apply to women.
(b) observational studies give only weak evidence for causation.
(c) the people who took vitamins may have had other good habits.
(d) the response is measured in a biased way.
(e) nonsampling errors may be large.
24. Medical experiments, such as one to compare aspirin with a placebo for preventing heart
attacks, are often double blind. This means that
(a) neither the subject nor the doctors know which treatment the patient received.
(b) subjects choose which treatment they get, but do not tell the doctors.
(c) the doctors choose which treatment to give each subject, but do not tell the subjects.
(d) subjects are not told either their treatment or their medical condition.
(e) all individual data are kept confidential.
64. The reason that block designs are sometimes used in experimentation is to
(a) prevent the placebo effect.
(b) allow double blinding.
(c) eliminate confounding with another factor.
(d) eliminate sampling variability.
(e) involved a large number of subjects.
25. You wonder whether drinking coffee before a statistics exam improves the performance of
students on the exam. The best way to get good evidence of the effect of coffee on exam scores is
(a) Find out which students drink coffee before the exam and which do not; compare their exam
scores.
(b) Take an opinion poll, asking students if they think coffee helps them stay alert.
(c) Get your friends to drink coffee before Exam 1 but not before Exam 2; compare their scores
on the two exams.
(d) Assign some students, chosen at random, to drink coffee and others to avoid coffee
before the exam; compare their exam scores.
(e) Take blood pressure measurements on some student before and after they drink some coffee.
26. Two essential features of all statistically designed experiments are
(a) compare several treatments; use the double-blind method.
(b) compare several treatments; use chance to assign subjects to treatments.
(c) always have a placebo group; use the double-blind method.
(d) use a block design; use chance to assign subjects to treatments.
(e) use a block design; replace dropouts and non-adherents
27. In the setting of the previous question, preliminary information suggests that the effect of
calcium is larger for black men than for white men. Knowing this, you would probably use
(a) a stratified random sample.
(b) a completely randomized design.
(c) a block design, with calcium and placebo as the blocks.
(d) a block design, with black men in one block and white men in the other.
(e) a block design, with half the black men and half the white men in one block and the rest in
the other block.
28. In the experiment of the previous questions, neither the subjects nor the doctors who work
with them know whether or not a subject was given extra calcium. This is called
(a) informed consent.
(b) randomization.
(c) the double-blind technique.
(d) confounding.
(e) blocking
29. A study shows that patients who receive surgery for intestinal cancer live much longer after
treatment than patients who are treated without surgery. But doctors operate only on patients in
relatively good condition, so we can't conclude that surgery lengthens the patients' lives. This is
an example of
(a) double-blind technique.
(b) internal inconsistency.
(c) the placebo effect.
(d) confounding.
(e) voluntary response.
A farmer wishes to determine which of two brands of baby-pig pellets, Kent or Moormans,
produces better weight gains. Two of his sows each give birth to litters of 10 pigs on the same
day, so he decides to give the baby-pigs in litter A only Kent pellets, while the pigs in litter B
will get only Moormans pellets. After four weeks, the average weight gain for pigs in litter A is
greater than the average weight gain for pigs in litter B. The next five questions concern this study.
30. The farmer in this story has conducted
(a) a stratified random sample.
(b) a matched pair design.
(c) an observational study.
(d) an experiment.
(e) a double-blind trial.
31. In the farmer story above, the weight of the pigs after four weeks is
(a) a parameter.
(b) the response variable.
(c) the explanatory variable.
(d) the placebo effect.
(e) stratified.
32. The brand of pellets in this story is
(a) a parameter.
(b) the response variable.
(c) the explanatory variable.
(d) the placebo effect.
(e) stratified.
33. The feed they get is not the only factor affecting the rate at which pigs gain weight. Genetic
differences also affect weight gain. It is likely that the pigs in litter A are genetically different
from the pigs in litter B, since the two litters have different mothers. Since the farmer is only
interested in determining which brand of pellets is better, the study suffers from
(a) confounding
(b) voluntary response.
(c) convenience sampling.
(d) invalid measurement.
(e) the placebo effect.
34. If the farmer had fed Kent pellets to an SRS of 5 pigs from litter A and an SRS of 5 pigs from
litter B, with the remaining 10 pigs getting Moormans pellets, then he would have been using
(a) a systematic random sample.
(b) a convenience sample.
(c) a matched-pairs design.
(d) a block design.
(e) a completely randomized design.
35. Randomization in experimental design is used to
(a) control for the response variable.
(b) avoid confounding.
(c) avoid the placebo effect.
(d) implement the double-blind technique.
(e) reduce the impact of dropouts and non-adherents
36. The basic ethical requirements for any study of human subjects are
(a) comparison, randomization, and replication.
(b) approval by a review board, informed consent, confidentiality of data.
(c) subjects are anonymous, subjects are randomly chosen, subjects cannot be harmed.
(d) data production, data analysis, inference.
(e) both (b) and (c)
37. All statistical studies should follow the principle of confidentiality. This means that
(a) information about individual subjects is never made public.
(b) the identities of the subjects are not known even to the researchers.
(c) information about who paid for the study is never made public.
(d) the results and conclusions of the study are never made public.
(e) neither the subjects nor the people who have contact with them should know which
experimental group each subject is in.
38. Any institution that does research with human subjects must have an Institutional Review
Board. This board reviews all planned research with human subjects in advance in order to
(a) be sure that the research has some scientific value.
(b) be sure that the researchers are qualified to do the research.
(c) be sure that the research obeys all the standards that protect the human subjects from
harm.
(d) be sure that the statistical design of the research is sound, so that useful data will result.
(e) all of the above.
39. Any sample survey should follow these two basic principles of data ethics:
(a) Anonymity and random sampling.
(b) Comparison and randomization.
(c) Double-blind and placebo.
(d) Bias and variability.
(e) Informed consent and confidentiality.
40. Any statistical study that uses human subjects requires informed consent. This means that
(a) a review board must agree that the study is worthwhile and will not harm the subjects.
(b) the authors of the study must agree to inform the public of the study results.
(c) the authors of the study must agree to inform the subjects of the study results.
(d) the authors of the study must inform a review board about it and obtain the board's consent to
go ahead.
(e) the nature of the study must be explained in advance to the subjects and they must
voluntarily agree to take part.