Deck 5: Experiments, Good and Bad

Question 1

Does St. John's wort have a significant effect in treating major depression? A study looked at 340 adult outpatients suffering from major depression as measured by their HAM-D score, randomly assigning each subject to either a placebo, St. John's wort, or a second active treatment for comparison.
Why is this study an experiment? Because:

A) the researchers were comparing outcomes from three groups.
B) there is a response variable.
C) there was a placebo.
D) the researchers assigned treatments to the subjects.

Answer 1

the researchers assigned treatments to the subjects.

Question 2

Does St. John's wort have a significant effect in treating major depression? A study looked at 340 adult outpatients suffering from major depression as measured by their HAM-D score, randomly assigning each subject to either a placebo, St. John's wort, or a second active treatment for comparison.
The St. John's wort study doesn't show that St. John's wort is equivalent to a placebo. If the researchers still believe in the effectiveness of St. John's wort in treating depression, how might they change their study?

A) They should carefully choose which patients get the placebo and which get St. John's wort to guarantee significant results.
B) They should increase the sample size.
C) They should decrease the sample size.
D) They shouldn't have a placebo group; they should give all the subjects the St. John's wort so they can measure its effect more precisely.

Answer 2

They should increase the sample size.

Question 3

Do doctors in managed care plans give less charity care? Researchers chose 60 communities at random, then chose doctors at random in each community. In all, they interviewed 10,881 doctors. Overall, 77.3% of the doctors said they had given some care free or at reduced rates because of the patient's financial need in the month before the interview. Doctors who received at least 85% of their practice income from managed care plans were significantly less likely than other doctors to provide charity care.
This study is a(n)

A) randomized comparative experiment.
B) experiment, but there is no control group.
C) census.
D) sample survey.

Answer 3

sample survey.

Question 4

The article was headlined, "Two Cups of Coffee Can Reduce the Risk of Liver Disease, Study Finds." A meta-analysis, based on combining nine previous studies involving 430,000 individuals, concluded that consumption of two cups of coffee a day reduced the chance of cirrhosis of the liver by 44 percent; even greater consumption was found to further reduce the risk of the disease.
The explanatory variable in this study is:

A) incidence of cirrhosis of the liver.
B) coffee consumption.
C) There is no explanatory variable because it is a meta-analysis.
D) not given in the quote above.

Question 5

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 study is a(n):

A) randomized comparative experiment.
B) experiment, but without randomization.
C) simple random sample.
D) observational study, but not a simple random sample.

Question 6

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.
In this study, the explanatory variable is:

A) the volunteer's flexibility score.
B) whether the volunteer had a meditation session.
C) the placebo.
D) a lurking variable.

Question 7

Do doctors in managed care plans give less charity care? Researchers chose 60 communities at random, then chose doctors at random in each community. In all, they interviewed 10,881 doctors. Overall, 77.3% of the doctors said they had given some care free or at reduced rates because of the patient's financial need in the month before the interview. Doctors who received at least 85% of their practice income from managed care plans were significantly less likely than other doctors to provide charity care.
The phrase "significantly less likely" means that, when we compare the charity work of doctors with more than 85% of their practice in managed care with other doctors,

A) the difference in charity work is very large.
B) the difference in charity work is so large that it would rarely occur just by chance in choosing a sample.
C) the difference in charity work is large enough to affect doctors' incomes.
D) the difference in charity work is less than we would expect just by chance in choosing a sample.

Question 8

The article was headlined, "Two Cups of Coffee Can Reduce the Risk of Liver Disease, Study Finds." A meta-analysis, based on combining nine previous studies involving 430,000 individuals, concluded that consumption of two cups of coffee a day reduced the chance of cirrhosis of the liver by 44 percent; even greater consumption was found to further reduce the risk of the disease.
The response variable in this study is:

A) incidence of cirrhosis of the liver.
B) coffee consumption.
C) There is no response variable because it is a meta-analysis.
D) not given in the quote above.

Question 9

Does eating while driving make an accident more likely? Researchers from the National Highway Traffic Safety Administration looked at national traffic and accident records from a recent year for those drivers who were eating versus those who were not. Result: The odds of an accident were 80 percent higher when eating than when not.
An example of a lurking variable that might affect the results of this study is:

A) whether the subject had an auto accident.
B) whether the subject was eating.
C) whether the subject was talking to a passenger in the car.
D) whether the subject owned a cell phone.

Question 10

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.

Question 11

Does eating while driving make an accident more likely? Researchers from the National Highway Traffic Safety Administration looked at national traffic and accident records from a recent year for those drivers who were eating versus those who were not. Result: The odds of an accident were 80 percent higher when eating than when not.
The explanatory variable in this study is:

A) whether the subject had an auto accident.
B) whether the subject was eating.
C) the risk of an accident.
D) whether the subject owned a car.

Question 12

The drug manufacturer Merck recently stopped testing a promising new drug to treat depression. It turned out that in a randomized, double-blind trial a dummy pill did almost as well as the new drug. The fact that many people respond to a dummy treatment is called

A) confounding.
B) nonresponse.
C) comparison.
D) the placebo effect.

Question 13

Which of the following are the three principles of experimental design?

A) Confound, Randomize, Small Samples
B) Confound, Randomize, Large Samples
C) Control, Randomize, Small Samples
D) Control, Randomize, Large Samples

Question 14

Does St. John's wort have a significant effect in treating major depression? A study looked at 340 adult outpatients suffering from major depression as measured by their HAM-D score, randomly assigning each subject to either a placebo, St. John's wort, or a second active treatment for comparison.
The study found the difference in treating major depression as measured by improvement in HAM-D scores between St. John's wort and the placebo was not statistically significant. This means that:

A) we cannot make a 95 percent confidence statement.
B) a difference this big could easily occur just by chance even if St. John's wort does no better than the placebo.
C) the placebo makes no difference in the subjects' depression.
D) the study was badly designed.

Question 15

The most important advantage of experiments over observational studies is

A) experiments are usually easier to carry out.
B) a well-designed experiment can give good evidence that the treatments actually cause the response.
C) an experiment can compare two or more groups.
D) we can use randomization to avoid bias in designing an experiment.
E) we can study the relationship between two or more explanatory variables.

Question 16

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.
In this study, the response variable is:

A) the volunteer's flexibility score.
B) whether the volunteer had a meditation session.
C) the placebo.
D) a lurking variable.

Question 17

A researcher studied whether meeting regularly with a weight-loss counselor helps dieters lose weight. Eighty dieters were available for the study. Half the dieters, assigned at random, received weight-loss counseling. The other half did not. After six months, the weight lost by each dieter was measured. On the average, those who met regularly with a weight-loss counselor lost more weight than those who did not.
This study is a(n)

A) randomized comparative experiment.
B) experiment, but without randomization.
C) simple random sample.
D) observational study, but not an SRS.

Question 18

Does eating while driving make an accident more likely? Researchers from the National Highway Traffic Safety Administration looked at national traffic and accident records from a recent year for those drivers who were eating versus those who were not. Result: The odds of an accident were 80 percent higher when eating than when not.
This study is a(n):

A) experiment, but without randomization.
B) simple random sample.
C) observational study, but not a simple random sample.
D) randomized comparative experiment.

Question 19

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.
An example of a lurking variable that might affect the results of this study is:

A) whether the volunteer had a meditation session.
B) the time of day the test was administered.
C) whether the volunteer practiced yoga.
D) whether the volunteer was being paid to participate in the study.

Question 20

A researcher studied whether meeting regularly with a weight-loss counselor helps dieters lose weight. Eighty dieters were available for the study. Half the dieters, assigned at random, received weight-loss counseling. The other half did not. After six months, the weight lost by each dieter was measured. On the average, those who met regularly with a weight-loss counselor lost more weight than those who did not.
In order to create groups of subjects that should be similar, on average, in all respects, we use

A) lurking.
B) confounding.
C) randomization.
D) All of the above

Question 21

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:
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.

Question 22

A study compares the effect on college students of two different TV advertisements for spring break in Gulf Shores, Alabama. Call the ads "Ad #1" and "Ad #2." We want to know which ad makes more students want to visit Gulf Shores during spring break. The subjects are 90 students taking a course in hotel management. The design of the study looks like this: The response variable should be named in the outline at "Question C." The response variable in this study is

A) whether a student wants to visit Gulf Shores.
B) which advertisement a student watched.
C) 90 college students.
D) randomization.
E) Ad #2.

Question 23

Were the extinctions that occurred in the last ice age more frequent among species of animals with large body sizes? A researcher gathers data on the average body mass (in kilograms) of all species known to have existed at that time. What are the explanatory and response variables?

A) There is no explanatory-response distinction in this situation.
B) Explanatory: body mass of a species. Response: whether the species went extinct.
C) Explanatory: the ice age. Response: whether a species went extinct.
D) Explanatory: whether a species went extinct. Response: the body mass of the species.
E) Explanatory: the ice age. Response: the body mass of a species.

Question 24

A researcher claims that the mean resting pulse rate of all college basketball players in the United States is less than the mean resting pulse rate of all professional basketball players in the United States. The resting pulse rates of a random sample of 115 college basketball players were measured as were the resting pulse rates of a random sample of 80 professional basketball players. The mean resting pulse rates of the two groups were compared.
This study is a(n)

A) voluntary response.
B) observational study.
C) randomized comparative experiment.
D) experiment, but without randomization.

Question 25

A study compares the effect on college students of two different TV advertisements for spring break in Gulf Shores, Alabama. Call the ads "Ad #1" and "Ad #2." We want to know which ad makes more students want to visit Gulf Shores during spring break. The subjects are 90 students taking a course in hotel management. The design of the study looks like this: The method used to form the groups appears in the diagram above at the point marked "Question A." This method is

A) men in Group 1, women in Group 2.
B) students choose which group they want.
C) voluntary response.
D) randomization.
E) the first students to appear go to Group 1.

Question 26

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:
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) Divide and conquer
E) Stratified sampling

Question 27

A psychologist recently said that, "For relatively mild medical problems, the placebo effect will produce positive results in roughly two-thirds of patients." The placebo effect is

A) the bias due to voluntary response in a sample.
B) the effect of a dummy treatment on a patient.
C) a violation of comparative experimentation.
D) the effect of confounding in an observational study.

Question 28

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:
The label for the dummy pill treatment should appear in the outline at the point marked "Question B." What is this label?

A) Random allocation
B) Placebo
C) Vitamins
D) Cancer
E) Finnish men

Question 29

A study compares the effect on college students of two different TV advertisements for spring break in Gulf Shores, Alabama. Call the ads "Ad #1" and "Ad #2." We want to know which ad makes more students want to visit Gulf Shores during spring break. The subjects are 90 students taking a course in hotel management. The design of the study looks like this: A weakness of this study is that

A) this is an observational study, so we can't conclude that the ad viewed causes the response.
B) the design is biased in favor of Ad #1.
C) the design is biased against Ad #1.
D) because the students all come from one course, the findings may not extend to all college students.
E) there is no placebo group.

Question 30

A West Coast university statistics professor wishes to determine which surfboard brand delivers consistently longer rides, Channel Island or JS. He recruits two of his students who surf to assist in an experiment, and the student assigned to the Channel Island board is determined by coin flip. The three head out to the beach for an afternoon, with the professor holding up a sign at random times for the respective student to catch the next wave on his board, and the time spent on that wave is recorded. This is repeated until each student has ridden 10 waves.
The brand of surfboard in this story is:

A) a parameter.
B) the response variable.
C) the explanatory variable.
D) blinded.
E) stratified.

Question 31

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:
An example of a confounding variable that might affect the results of this study is

A) the brand of cigarette smoked.
B) the age of participant.
C) the brand of vitamin supplement.
D) none of the above because the subjects were divided up randomly, and any possible effects due to confounding variables should be balanced between the two groups.

Question 32

A West Coast university statistics professor wishes to determine which surfboard brand delivers consistently longer rides, Channel Island or JS. He recruits two of his students who surf to assist in an experiment, and the student assigned to the Channel Island board is determined by coin flip. The three head out to the beach for an afternoon, with the professor holding up a sign at random times for the respective student to catch the next wave on his board, and the time spent on that wave is recorded. This is repeated until each student has ridden 10 waves.
The brand of board they're riding on is not the only factor affecting the length of time they ride each wave. It is likely that the two surfing students are not identical in surfing ability. Since the professor is only interested in determining which surfboard brand delivers longer rides, the study suffers from:

A) confounding.
B) voluntary response.
C) convenience sampling.
D) invalid measurement.
E) the placebo effect.

Question 33

A study compares the effect on college students of two different TV advertisements for spring break in Gulf Shores, Alabama. Call the ads "Ad #1" and "Ad #2." We want to know which ad makes more students want to visit Gulf Shores during spring break. The subjects are 90 students taking a course in hotel management. The design of the study looks like this: What is Group 2's treatment (at the point marked "Question B" in the diagram)?

A) A placebo
B) Ad #2
C) One of the ads, chosen at random
D) Watch TV, but see no advertisement
E) Can't say because treatments were assigned at random

Question 34

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:
The response variable should be named in the outline at "Question C." The response variable in this study is

A) whether a subject took vitamins.
B) 29,000 Finnish men.
C) random allocation.
D) a confidence statement.
E) whether a subject developed cancer.

Question 35

A researcher claims that the mean resting pulse rate of all college basketball players in the United States is less than the mean resting pulse rate of all professional basketball players in the United States. The resting pulse rates of a random sample of 115 college basketball players were measured as were the resting pulse rates of a random sample of 80 professional basketball players. The mean resting pulse rates of the two groups were compared.
In this study, the response variable is

A) the level of basketball played (college or professional).
B) the number of players studied in each group.
C) the resting pulse rate.
D) confounded with the placebo effect.

Question 36

A study compares the effect on college students of two different TV advertisements for spring break in Gulf Shores, Alabama. Call the ads "Ad #1" and "Ad #2." We want to know which ad makes more students want to visit Gulf Shores during spring break. The subjects are 90 students taking a course in hotel management. The design of the study looks like this: The statistical name for this study design is

A) simple random sample.
B) stratified random sample.
C) randomized comparative experiment.
D) systematic sample.
E) observational study.

Question 37

A researcher claims that the mean resting pulse rate of all college basketball players in the United States is less than the mean resting pulse rate of all professional basketball players in the United States. The resting pulse rates of a random sample of 115 college basketball players were measured as were the resting pulse rates of a random sample of 80 professional basketball players. The mean resting pulse rates of the two groups were compared.
In this study, the explanatory variable is

A) the level of basketball played (college or professional).
B) the number of players studied in each group.
C) the resting pulse rate.
D) confounded with the placebo effect.

Question 38

A researcher claims that the mean resting pulse rate of all college basketball players in the United States is less than the mean resting pulse rate of all professional basketball players in the United States. The resting pulse rates of a random sample of 115 college basketball players were measured as were the resting pulse rates of a random sample of 80 professional basketball players. The mean resting pulse rates of the two groups were compared.
An example of a lurking variable that might affect the results of this study is

A) the team each player is from.
B) the location the study was administered.
C) whether or not the players had scholarships in college.
D) the age of the players.

Question 39

An important reason for the use of randomization in designing experiments is that it tends to

A) reduce confounding.
B) allow double-blinding.
C) eliminate response error.
D) reduce the placebo effect.

Question 40

A West Coast university statistics professor wishes to determine which surfboard brand delivers consistently longer rides, Channel Island or JS. He recruits two of his students who surf to assist in an experiment, and the student assigned to the Channel Island board is determined by coin flip. The three head out to the beach for an afternoon, with the professor holding up a sign at random times for the respective student to catch the next wave on his board, and the time spent on that wave is recorded. This is repeated until each student has ridden 10 waves.
In the surfing story above, the time spent on the wave is:

A) a parameter.
B) the response variable.
C) the explanatory variable.
D) randomized.
E) stratified.

Question 41

Does taking vitamins prevent colon cancer? A study assigned 864 subjects at random to four groups. One group took beta-carotene, another took vitamins C and E, a third took all three, and the fourth group took only a dummy pill. After four years, there was no difference among the groups in the formation of polyps in the colon that precede cancer.
Earlier studies had shown that people who choose to eat a lots of vegetables containing these vitamins tend to have less colon cancer.

A) The earlier studies are more convincing than the new study because they involved thousands of people.
B) The results of the earlier studies could be due to some other fact about people who choose to eat a lot of vegetables.
C) The new study is more convincing because people were assigned to treatments at random, rather than choosing whether or not to take vitamins.
D) Both B and C are correct.
E) Answers A, B, and C are correct.

Question 42

An observed effect that is of a size that would rarely occur by chance is called

A) a randomized effect.
B) the confounding effect.
C) a statistically significant effect.
D) the placebo effect.

Question 43

An experiment on the effect of vitamin A on cancer uses two randomly chosen groups of 200 men each, one given vitamin A and the other a placebo. An estimate from a similar experiment using two groups of 1000 men each would have

A) less bias.
B) more bias.
C) more variability.
D) less variability.

Question 44

A recent issue of the New England Journal of Medicine reports a study of all 122,754 infants born over an 8.5-year period at Parkland Hospital in Dallas, leaving out multiple births and infants with birth defects. The researchers wanted to know if there is a specific birth weight below which infant death and illness increases sharply.
The explanatory variable in the study is

A) death and illness.
B) birth weight.
C) infants (leaving out multiple births, etc.).
D) Parkland Hospital.
E) 122,754.

Question 45

Does taking vitamins prevent colon cancer? A study assigned 864 subjects at random to four groups. One group took beta-carotene, another took vitamins C and E, a third took all three, and the fourth group took only a dummy pill. After four years, there was no difference among the groups in the formation of polyps in the colon that precede cancer.
Does the new study (properly designed) give good reason to think that vitamins prevent colon cancer?

A) Yes, randomized comparative experiments give good evidence for causation
B) No, there was no significant difference among the groups.
C) Yes, a study incorporating a placebo gives good evidence for causation.
D) No, this is an observational study.

Question 46

A magazine article on preventing cancer says, "Eating one serving of tofu a week may cut your risk of breast cancer 15%, recent research suggests."
If 15% is a statistically significant amount, then

A) the results must be false.
B) this study must have been an experiment.
C) tofu prevents breast cancer.
D) the results probably did not occur by chance.

Question 47

A magazine article on preventing cancer says, "Eating one serving of tofu a week may cut your risk of breast cancer 15%, recent research suggests."
The data come from an observational study; therefore,

A) the results must be false.
B) the results must be true.
C) there may be lurking variables.
D) perhaps those who chose to eat more tofu are, for some reason, less susceptible to breast cancer than those who didn't.
E) Both C and D are correct.

Question 48

Hearing loss is more common among premature infants than among full-term infants. This was thought to be an effect of premature birth. It has recently been suggested that hearing loss may be caused by the high noise level of the incubators in which the premature infants are placed. This is an example of

A) statistical significance.
B) confounding between two variables.
C) a designed experiment.
D) nonrandom sampling error.
E) matching.

Question 49

A recent issue of the New England Journal of Medicine reports a study of all 122,754 infants born over an 8.5-year period at Parkland Hospital in Dallas, leaving out multiple births and infants with birth defects. The researchers wanted to know if there is a specific birth weight below which infant death and illness increases sharply.
This study is a(n)

A) randomized comparative experiment.
B) experiment, but subjects are not assigned at random.
C) probability sample of a population.
D) observational study, but not a probability sample.
E) stratified sample.

Question 50

One method that can be used to avoid problems with confounding variables in observational studies is to

A) match similar subjects from each of the study groups for comparisons.
B) randomly assign subjects to study groups.
C) use very large samples.
D) use voluntary response sampling.