Deck 6: Experiments in the Real World

Question 1

Which of the following statements about a randomized block design with two treatments is not true?

A) Every subject has a 50/50 chance of being given the first treatment.
B) Block A is chosen randomly from among the available subjects.
C) In every block, some subjects are assigned the first treatment and some the second treatment.
D) Treatments are assigned randomly within each block.

Answer 1

Block A is chosen randomly from among the available subjects.

Question 2

You work for an agricultural supply company that is investigating a new fertilizer for soybeans. You have been asked to design an experiment to compare the effectiveness of three different application amounts of the fertilizer to find the optimal amount. Each field of soybeans will be fertilized with one of the application amounts (to be determined randomly). You think there may be large differences among different farms because of soil quality. Because of these differences, you should use a

A) completely randomized design.
B) categorical variable.
C) block design.
D) matched pairs design.
E) multistage sample.

Answer 2

block design.

Question 3

Two essential features of all statistically designed experiments are that they

A) compare several treatments and use the double-blind method.
B) compare several treatments and use chance to assign subjects to treatments.
C) always have a placebo group and use the double-blind method.
D) use a block design and use chance to assign subjects to treatments.

Answer 3

compare several treatments and use chance to assign subjects to treatments.

Question 4

A recent medical study found that people who drink more than four cups of coffee a day have more heart attacks than people who drink less coffee or no coffee. This led some doctors to suspect that coffee may be a contributing factor in causing heart attacks. However, more careful analysis of the data showed that heavy coffee drinkers tend to smoke more than other people. This is an example of

A) the placebo effect.
B) response error.
C) the double-blind technique.
D) a completely randomized design.
E) confounding.

Question 5

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, selected at random, 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 study design looked like this:
Treatment 2 was a dummy pill. Such a dummy treatment is called a

A) double-blind technique.
B) categorical variable.
C) nonsampling error.
D) placebo.
E) comparative.

Question 6

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.

Question 7

To control for the possible lurking variables when assigning subjects to the experiment's treatments, use:

A) a placebo and double blinding.
B) blocking and randomization.
C) probability sampling and confounding.
D) explanatory and response variables.

Question 8

Volunteers for a human performance study were randomly divided into two groups. The first group had their flexibility measured in the morning after a short meditation session while the second group had their flexibility measured in the afternoon with no previous meditation session. The flexibility scores of the two groups were compared.
This experiment was not double-blind because:

A) volunteers were allowed to keep their eyes open while having their flexibility measured.
B) the volunteers knew the whether they had meditated before having their flexibility measured.
C) some of the volunteers stretched before they went to the study location.
D) volunteers were randomized into the two groups.

Question 9

It is 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

Question 10

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, selected at random, 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 study design looked like this:
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.

Question 11

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, selected at random, 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 study design looked like this:
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.

Question 12

A professor believes that students who smoke cigarettes tend to have lower grades. He collects data from 1326 randomly selected students at his university and discovers that, on average, students who smoke cigarettes do indeed tend to have lower grade point averages than students who do not smoke.
This study was based on

A) a randomized comparative experiment.
B) a matched pairs experiment.
C) a voluntary response sample.
D) a probability sample.

Question 13

A study of a drug to prevent hair loss showed that 86% of the men who took it maintained or increased the amount of hair on their heads. But so did 42% of the men in the same study who took a placebo instead of the drug. This is an example of

A) a sampling error: The study should not have included men whose hair grew without the drug.
B) the placebo effect.
C) an error in calculating percentages.
D) failure to use the double-blind idea.

Question 14

Volunteers for a human performance study were randomly divided into two groups. The first group had their flexibility measured in the morning after a short meditation session while the second group had their flexibility measured in the afternoon with no previous meditation session. The flexibility scores of the two groups were compared.
To improve the design of this experiment, one part of it should be done in a blind way. That is, we should:

A) not tell volunteers in advance what treatment they may be exposed to.
B) not allow the volunteers to find out their flexibility scores.
C) tell all of the volunteers who meditate they will get a gym membership if they work very hard on the flexibility test.
D) be sure that the person measuring the volunteers' flexibility doesn't know which ones meditated and which ones didn't.

Question 15

Volunteers for a human performance study were randomly divided into two groups. The first group had their flexibility measured in the morning after a short meditation session while the second group had their flexibility measured in the afternoon with no previous meditation session. The flexibility scores of the two groups were compared.
The study design for this experiment is called a(n):

A) simple random sample design.
B) completely randomized design.
C) matched pairs design.
D) randomized block design.
E) observational study.

Question 16

The reason that block designs are sometimes used in experimentation is to

A) prevent the placebo effect.
B) allow double-blinding.
C) reduce sampling variability.
D) eliminate sampling variability.

Question 17

A farmer wishes to determine which of two brands of baby-pig pellets, Kent or Moormans, produces better weight gain. 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 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.
What experimental design technique could the farmer use to take into account the genetic differences?

A) Placebo
B) Blocking
C) Probability sampling
D) Double blinding
E) Observational study

Question 18

Does Stay Bright nail polish remain on fingernails longer than Acme nail polish? You design an experiment to find out. A random sample of people was selected to wear both nail polishes. Which hand received which polish was determined randomly. After one week, the difference in the quality of the nail polish of each subject is evaluated. What type of experimental design is this?

A) This is a nonrandomized design.
B) This is a matched pairs design.
C) This is a completely randomized design with one factor.
D) This is a completely randomized design with two factors.
E) This is an observational study.

Question 19

A park ranger at Shenandoah National park wants to know if visitors to our country's national parks can properly identify poison ivy. Over the course of a month, she shows several plant varieties to 30 randomly selected visitors per week, and 74 of them correctly identify the poison ivy. The biggest potential weakness of experiments is that:

A) experiments do not give good evidence for cause and effect.
B) experiments only work when one can give a placebo.
C) it can be hard to generalize conclusions beyond the actual subjects to a wider population.
D) informed consent is often not possible.

Question 20

A professor believes that students who smoke cigarettes tend to have lower grades. He collects data from 1326 randomly selected students at his university and discovers that, on average, students who smoke cigarettes do indeed tend to have lower grade point averages than students who do not smoke.
Does this study give strong evidence that smoking cigarettes causes lower grades?

A) Yes, because the study included both people who smoked and people who didn't.
B) Yes, because the subjects in the study were selected at random.
C) No, because the study showed that there is no connection between smoking and grades.
D) No, because people who make bad decisions may choose not to study well and may choose to smoke cigarettes.
E) No, because the people in the study were not blinded.

Question 21

The keys to convincing experiments are

A) randomization, double-blind technique, and comparison of several treatments.
B) randomization, adequate numbers, and double-blind technique.
C) control, sampling distributions, and double-blind technique.
D) confidence intervals, adequate numbers, and comparison of several treatments.
E) randomization, control, and adequate numbers.

Question 22

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.

Question 23

The difference between an experiment and an observational study is that

A) observational studies don't have explanatory and response variables.
B) experiments don't have placebos.
C) an experiment imposes treatments on subjects, while an observational study accepts existing treatments.
D) experiments are double-blind, while observational studies are only single-blind.
E) All of the above

Question 24

A scientist is designing a clinical trial to test the effect of online chat counseling with migraine sufferers as a supplementary treatment in combating their migraines. Migraine sufferers will have access to counselors via online chat software; the scientist plans to see whether their migraine pain has been reduced after six weeks.
The subjects would obviously know whether or not they were given access to the counseling. What experimental technique does this eliminate?

A) informed consent
B) randomization
C) blinding
D) confounding

Question 25

We say that the design of a study is biased if which of the following is true?

A) We suspect racial or sexual prejudice.
B) The study assigns subjects at random to a placebo.
C) The study systematically favors certain outcomes.
D) The study fails to use blocking.
E) The study is double-blind.

Question 26

To see if eating just before going to bed causes nightmares, volunteers are recruited to spend the night in a sleep laboratory while connected to machines that monitor their sleep patterns. They are randomly assigned to be given a meal before bed or not. Numbers of nightmares are recorded and compared for the two groups. The critics claim the study

A) gives results that do not generalize.
B) does not use a placebo.
C) is not precise.
D) cannot establish causation because it is an observational study.

Question 27

In a randomized block design the blocks often represent levels of

A) a lurking variable suspected of being confounded with the explanatory variable.
B) the explanatory variable.
C) the response variable.
D) placebo dosage.

Question 28

In comparative drug studies, double-blind experiments are typically used. The purpose of keeping the diagnosing physicians ignorant of the treatment status of the experimental subjects is to

A) eliminate grounds for malpractice suits.
B) ensure that subjects were randomly assigned to treatments.
C) eliminate a possible source of bias.
D) make sure nobody is harmed.
E) prevent stratification of the experiment.

Question 29

A scientist is designing a clinical trial to test the effect of online chat counseling with migraine sufferers as a supplementary treatment in combating their migraines. Migraine sufferers will have access to counselors via online chat software; the scientist plans to see whether their migraine pain has been reduced after six weeks.
Preliminary information suggests that the effect of (face-to-face) counseling is larger for migraine sufferers who are women than men. Knowing this, the scientist would probably use a:

A) stratified random sample.
B) completely randomized design.
C) block design, with counseling and no counseling as the blocks.
D) block design, with women and men as the blocks.

Question 30

A music professor offers his 40 students the option of coming to an additional rehearsal session the week before their juries (musical final exams.) In order to decide whether these extra sessions actually help students, he keeps track of who attends them and compares their jury scores to those of students who did not schedule extra sessions.
This study is a(n):

A) observational study.
B) nonrandomized experiment.
C) completely randomized experiment.
D) randomized block design.
E) matched pairs design.

Question 31

A music professor offers his 40 students the option of coming to an additional rehearsal session the week before their juries (musical final exams.) In order to decide whether these extra sessions actually help students, he keeps track of who attends them and compares their jury scores to those of students who did not schedule extra sessions.
In this study, a difference was found between the scores of students who scheduled the extra sessions and those of students who didn't attend (higher average for students with extra sessions). Does this study give evidence that attending the review session leads to higher grades on their juries?

A) Yes, because the study included both students who attended the review session and those who did not.
B) Yes, because the number of subjects in the study was large.
C) Yes, because the study relied on a common final exam for everyone.
D) No, because the students chose whether they attended the review session or not.
E) No, because the students in the study were not blinded.

Question 32

A scientist is designing a clinical trial to test the effect of online chat counseling with migraine sufferers as a supplementary treatment in combating their migraines. Migraine sufferers will have access to counselors via online chat software; the scientist plans to see whether their migraine pain has been reduced after six weeks.
If the trial doesn't include a control group, the data will be invalid because of:

A) the placebo effect.
B) lack of confidentiality.
C) the double-blind effect.
D) voluntary response.