Deck 7: Designing Experiments

Question 1

Noroviruses cause roughly 21 million cases of gastroenteritis ("stomach flu") annually in the United States. A study examined the effectiveness of a new norovirus vaccine. Healthy adult volunteers received, at random, either the vaccine or a placebo. They were then exposed to the norovirus. In all, 14 of the 38 vaccinated subjects suffered from gastroenteritis, compared with 27 of the 39 subjects who received a placebo. Which type of study is this?

A)Case-control observational study
B)Matched pairs or repeated measures experiment
C)Completely randomized experiment
D)Experiment with a block design

Answer 1

C

Question 2

Are patches more effective than oral medication in helping individuals stop smoking? Two researchers randomly assigned 22 people to one of the two treatment groups (11 people were assigned to each group). The subjects were monitored for six weeks, during which they received treatment every day-a new patch for subjects in the first group and a single pill for subjects in the second group. The researchers reported that subjects wearing the patches were less likely to quit smoking, although the difference was not statistically significant. Which type of study is this?

A)Convenience sample
B)Observational study
C)Experiment, but not a double-blind experiment
D)Double-blind experiment

Answer 2

C

Question 3

A researcher is interested in investigating the relationship between sugar consumption and weight gain for high school students. Fifteen volunteers were randomly assigned to one of two groups. The first group contained six volunteers who were put on a low-sugar diet. The second group consisted of the remaining nine volunteers, who were put on a diet in which sugar constituted approximately 15% of their calories consumed. After eight weeks, the change in weight was recorded for each of the volunteers.
What is the response variable in this study?

A)Percent of sugar in the diet
B)Eight-week time period
C)Assignment to groups
D)Change in weight

Answer 3

D

Question 4

A researcher is interested in investigating the relationship between sugar consumption and weight gain for high school students. Fifteen volunteers were randomly assigned to one of two groups. The first group contained six volunteers who were put on a low-sugar diet. The second group consisted of the remaining nine volunteers, who were put on a diet in which sugar constituted approximately 15% of their calories consumed. After eight weeks, the change in weight was recorded for each of the volunteers.
What is the explanatory variable?

A)Percent of sugar in the diet
B)Eight-week time period
C)Assignment to groups
D)Change in weight

Question 5

A researcher is interested in investigating the relationship between sugar consumption and weight gain for high school students. Fifteen volunteers were randomly assigned to one of two groups. The first group contained six volunteers who were put on a low-sugar diet. The second group consisted of the remaining nine volunteers, who were put on a diet in which sugar constituted approximately 15% of their calories consumed. After eight weeks, the change in weight was recorded for each of the volunteers.
Which type of study is this?

A)Randomized observational study
B)Matched pairs experiment
C)Case-control study
D)Randomized comparative experiment

Question 6

A researcher is interested in investigating the relationship between sugar consumption and weight gain for high school students. Fifteen volunteers were randomly assigned to one of two groups. The first group contained six volunteers who were put on a low-sugar diet. The second group consisted of the remaining nine volunteers, who were put on a diet in which sugar constituted approximately 15% of their calories consumed. After eight weeks, the change in weight was recorded for each of the volunteers.
Which of the following principles of experimentation are used in this study?

A)Randomization
B)Confounding
C)Blocking
D)All of these answers are correct.

Question 7

Ability to grow in shade may help pine trees found in the dry forests of Arizona resist drought. To test this hypothesis, investigators planted pine seedlings in a greenhouse in full light, light reduced to 25% of normal, or light reduced to 5% of normal. At the end of the study, they dried the young trees and weighed them.
What are the treatments in this study?

A)Full light and full shade
B)Full light, light reduced to 25% of normal, and light reduced to 5% of normal
C)Different weights of the dried trees
D)The greenhouse and Arizona forests

Question 8

Ability to grow in shade may help pine trees found in the dry forests of Arizona resist drought. To test this hypothesis, investigators planted pine seedlings in a greenhouse in full light, light reduced to 25% of normal, or light reduced to 5% of normal. At the end of the study, they dried the young trees and weighed them.
What is the response variable in this study?

A)The shade and the light
B)The dry weights of the young trees
C)The dry forests of Arizona
D)The difference between greenhouse trees and trees in Arizona forests

Question 9

Ability to grow in shade may help pine trees found in the dry forests of Arizona resist drought. To test this hypothesis, investigators planted pine seedlings in a greenhouse to a randomly assigned light intensity: full light, light reduced to 25% of normal, or light reduced to 5% of normal. At the end of the study, they dried the young trees and weighed them.
Which type of study is this?

A)Stratified observational study
B)Matched pairs experiment
C)Completely randomized experiment
D)Block experiment

Question 10

Which of the following is NOT a fundamental principle of experimental design?

A)Randomization
B)Using enough subjects (or experimental units)
C)Comparing treatments
D)Eliminating variability

Question 11

Which term applies to any experimental condition applied to the subjects?

A)Experimental unit
B)Response variable
C)Treatment
D)Predictor variable

Question 12

A researcher was studying how the weights of horseshoe crabs along the East Coast vary between northern and southern habitats. In spring 2006, during breeding season, the researcher randomly selected 50 horseshoe crabs in southern habitats. In fall 2006, before the breeding season began, the researcher randomly selected 50 horseshoe crabs from northern habitats. It was found that crabs in southern habitats weighed more, so the researcher claimed that location had an effect on the weight of horseshoe crabs. Why should the results of this study not be trusted?

A)The study was not double-blind.
B)The investigator was biased. She knew beforehand what the study would show.
C)The investigator should have used more than two locations.
D)The time of year during which the samples were taken is a confounding variable.

Question 13

Does fibrolytic enzyme level in feedlot cattle affect cattle weight gain? Researchers randomly assigned 20 feedlot cattle to four groups, with each group being fed a diet containing a different enzyme level. Cattle weight gain (in kilograms) was recorded over the length of the study. Which type of study design was used?

A)Case-control observational study
B)Matched pairs or repeated measures experiment
C)Completely randomized experiment
D)Experiment with a block design

Question 14

The drug valproate has been shown in mice to facilitate adult learning of skills typically acquired during early life. A study enrolled healthy adult human males with no advanced musical training and taught them to identify absolute pitch, a rare ability typically learned in early childhood. In a first stage, the participants were randomly assigned to valproate or a placebo. In a second stage, the conditions were reversed, so that a participant who received the placebo first took valproate for the second stage, and vice versa. Which type of study design was used?

A)Case-control observational study
B)Matched pairs or repeated measures experiment
C)Completely randomized experiment
D)Experiment with a block design

Question 15

What does it mean when two variables are "confounded"?

A)Their effects on the response variable cannot be separated.
B)They are highly correlated.
C)They are only slightly correlated.
D)One of them is a placebo.

Question 16

The Physicians' Health Study followed 22,000 male physicians for a period of several years. Approximately 11,000 took an aspirin every second day, while the rest took a placebo. At the completion of the study, it was noted whether a subject had experienced a heart attack during the period of the study. It was found that the aspirin group had significantly fewer heart attacks than the placebo group.
Which factor was used in this experiment?

A)Severity of the heart attack
B)Use of a placebo
C)Medication used (aspirin or placebo)
D)Length of the study

Question 17

The Physicians' Health Study followed 22,000 male physicians for a period of several years. Approximately 11,000 took an aspirin every second day, while the rest took a placebo. At the completion of the study, it was noted whether a subject had experienced a heart attack during the period of the study. It was found that the aspirin group had significantly fewer heart attacks than the placebo group.
What is the response variable in this experiment?

A)Whether a heart attack occurred
B)The placebo effect
C)Whether the symptoms lessened
D)The length of the study

Question 18

A study attempts to determine whether a new medication is effective at lowering blood pressure. Forty subjects with hypertension who volunteer to participate in the study are to be given both the new medication and a placebo. The order in which each subject receives the treatment is randomized, and the subjects do not know which treatment they are getting. Each treatment is administered for four weeks. At the end of each four-week period, a subject's blood pressure is recorded.
What is described in this scenario?

A)A matched pairs experiment
B)A double-blind observational study
C)A stratified sample
D)The placebo effect

Question 19

A study attempts to determine whether a new medication is effective at lowering blood pressure. Forty subjects with hypertension who volunteer to participate in the study are to be given both the new medication and a placebo. The order in which each subject receives the treatment is randomized, and the subjects do not know which treatment they are getting. Each treatment is administered for four weeks. At the end of each four-week period a subject's blood pressure is recorded.
What are the experimental units in this study?

A)The medication taken by the 40 subjects who volunteered.
B)The 40 subjects who volunteered
C)The subjects who experienced a reduction of blood pressure
D)The subjects who didn't experience a significant reduction in blood pressure.

Question 20

Which of the following is an example of a matched pairs design?

A)Migraine-suffering patients receive aspirin one week and a new painkiller combination another week. The treatment order is randomized.
B)One set of teenagers get a topical fluoride application, while their twins don't. Which twin gets the fluoride treatment is randomly assigned for each twin pair.
C)In a study of diet and genetics, researchers assign randomly two rat pups from the same litter to be fed either a high-fat diet or a high-fiber diet. In all, the study used a dozen rat litters.
D)All of these answers are correct.

Question 21

A study recruited 48 overweight adults aged 55 to 75 years, and randomly divided them into two groups. Participants in one group drank 2 cups of water prior to their meals; the other group did not. All participants ate a low-calorie diet during the study. Over the course of 12 weeks, water drinkers lost about 15.5 pounds, while the non-water drinkers lost about 11 pounds, on average.
Which type of study is this?

A)Case-control observational study
B)Matched pairs or repeated-measures experiment
C)Completely randomized experiment
D)Placebo-controlled experiment

Question 22

A study recruited 48 overweight adults aged 55 to 75 years, and randomly divided them into two groups. Participants in one group drank 2 cups of water prior to their meals; the other group did not. All participants ate a low-calorie diet during the study. Over the course of 12 weeks, water drinkers lost about 15.5 pounds, while the non-water drinkers lost about 11 pounds, on average.
What is the response variable in this study?

A)Weight lost (in pounds)
B)Number of cups of water drunk before meals
C)Age (in years)
D)Being overweight (yes/no)

Question 23

Which of the following does NOT describe a treatment?

A)A specific experimental condition applied to the subjects
B)A combination of specific values of each factor
C)A response variable
D)A placebo

Question 24

A study recruited 48 overweight adults aged 55 to 75 years, and randomly divided them into two groups. Participants in one group drank 2 cups of water prior to their meals; the other group did not. All participants ate a low-calorie diet during the study. Over the course of 12 weeks, water drinkers lost about 15.5 pounds, while the non-water drinkers lost about 11 pounds, on average.
Here is a quote from the published study: "Due to an unintended greater random allocation of men to the water group than the non-water group, additional analyses were performed to determine if weight loss outcomes differed between men and women in the two groups." Based on this study, which of the following is true?

A)Gender is a confounding variable.
B)Gender is the response variable.
C)The study is biased in favor of men.
D)All participants should have been male.

Question 25

A study examined the effect of garlic on blood cholesterol levels. A total of 192 subjects with starting low-density lipoprotein (LDL) cholesterol ("bad cholesterol") levels between 130 and 190 mg/dl were randomly assigned to one of four treatments for six months: raw garlic eaten daily, a powdered garlic supplement taken daily (Garlicin brand), an aged-garlic extract taken daily (Kyolic brand), or a placebo pill taken daily. The study found no significant or clinical differences in blood cholesterol levels between the four groups at the end of the study.
Which type of study is this?

A)Stratified comparative survey
B)Completely randomized experiment
C)Matched pairs experiment
D)Stratified experiment

Question 26

A study examined the effect of garlic on blood cholesterol levels. A total of 192 subjects with starting low-density lipoprotein (LDL) cholesterol ("bad cholesterol") levels between 130 and 190 mg/dl were randomly assigned to one of four treatments for six months: raw garlic eaten daily, a powdered garlic supplement taken daily (Garlicin brand), an aged-garlic extract taken daily (Kyolic brand), or a placebo pill taken daily. The study found no significant or clinical differences in blood cholesterol levels between the four groups at the end of the study.
What were the subjects in the study?

A)The 192 individuals with starting LDL levels between 130 and 190 mg/dl
B)The individuals eating raw garlic for six months
C)All individuals with LDL levels between 130 and 190 mg/dl
D)All individuals with LDL levels between 130 and 190 mg/dl who eat garlic

Question 27

A study examined the effect of garlic on blood cholesterol levels. A total of 192 subjects with starting low-density lipoprotein (LDL) cholesterol ("bad cholesterol") levels between 130 and 190 mg/dl were randomly assigned to one of four treatments for six months: raw garlic eaten daily, a powdered garlic supplement taken daily (Garlicin brand), an aged-garlic extract taken daily (Kyolic brand), or a placebo pill taken daily. The study found no significant or clinical differences in blood cholesterol levels between the four groups at the end of the study.
What are the explanatory and response variables, respectively?

A)Treatment type and cholesterol level
B)Garlic supplement and placebo
C)Initial LDL level and final cholesterol level
D)Time and cholesterol level

Question 28

A study examined the effect of garlic on blood cholesterol levels. A total of 192 subjects with starting low-density lipoprotein (LDL) cholesterol ("bad cholesterol") levels between 130 and 190 mg/dl were randomly assigned to one of four treatments for six months: raw garlic eaten daily, a powdered garlic supplement taken daily (Garlicin brand), an aged-garlic extract taken daily (Kyolic brand), or a placebo pill taken daily. The study found no significant or clinical differences in blood cholesterol levels between the four groups at the end of the study.
Which of the following principles of experiments was used in this study?

A)Randomization
B)Blinding
C)Blocking
D)All of these answers are correct.

Question 29

One hundred volunteers who have agoraphobia are available for a study. Fifty are selected at random and are given the drug imipramine, which is believed to be effective in treating agoraphobia. The other 50 are given a placebo. A psychiatrist evaluates the symptoms of all volunteers after two months to determine if there has been substantial improvement in the severity of their symptoms.
Suppose the volunteers were first divided into men and women, and then half of the men were randomly assigned to the new drug and half of the women were assigned to the new drug. The remaining volunteers received the placebo. What would this be an example of?

A)Replication
B)Confounding; the effects of gender will be mixed up with the effects of the drugs
C)Block design
D)Matched pairs design

Question 30

Avandia is an antidiabetic drug. In a study of tolerance and side effects of Avandia, 428 patients with prediabetes were given 4 mg of Avandia daily for 26 weeks. The researchers compared the patients' baseline cholesterol levels at the beginning of the study with their level after the 26 weeks of treatment. The results show a significant increase in their low-density lipoprotein (LDL) cholesterol ("bad cholesterol") level.
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This is an example of

A)a retrospective, case-control observational study.
B)a prospective, cohort observational study.
C)a completely randomized experiment.
D)a matched pairs experiment.

Question 31

A total of 6972 homosexual and bisexual men have been enrolled since April 1984 in an ongoing study of HIV/AIDS. Participants are contacted twice a year to answer detailed lifestyle and medical questionnaires and provide a blood sample.
Which type of study design is being used?

A)Retrospective, case-control observational study
B)Prospective, cohort observational study
C)Completely randomized experiment
D)Matched pairs experiment

Question 32

A study examined how homing pigeons find their way home from distant and unfamiliar places, using a small GPS device attached to the birds. Each homing pigeon was trained to home from a site with striking landmarks as well as from a barren site with few visual landmarks. The GPS-recorded flight paths of the pigeons on the last release from each site showed a more direct route was taken when the birds homed from the site with striking landmarks.
Which type of study is this?

A)Case-control observational study
B)Cohort observational study
C)Completely randomized experiment
D)Matched pairs or repeated measures experiment

Question 33

A study of the occupational exposure to HIV among health care workers recruited 33 health care workers who had become HIV-seropositive after exposure to HIV at work and 665 health care workers who had been exposed to HIV but had not become seropositive. The study found that contaminated health care workers were more likely to have been exposed to large amounts of blood and less likely to have taken the drug AZT immediately after exposure than those who had not become seropositive.
Which type of study design is this?

A)Retrospective, case-control observational study
B)Prospective, cohort observational study
C)Completely randomized experiment
D)Matched pairs experiment

Question 34

A study randomly assigned subjects to receive either St. John's wort extract (n = 98) or a placebo (n = 102). For each subject, the investigators assessed the person's rate of change in the Hamilton Rating Scale for Depression over the treatment period.
Which type of study is this?

A)Stratified observational study
B)Case-control observational study
C)Completely randomized experiment
D)Block experiment

Question 35

A researcher conducts a study to investigate the effect of exercise and diet on mood. What are the factors in this study?

A)Whether randomization and placeboes were used
B)Whether the experiment was double-blind
C)The number of subjects
D)Exercise and diet

Question 36

Consumer Reports compared the effectiveness of an antiwrinkle cream with that of a plain moisturizer in reducing the appearance of wrinkles. The researchers enrolled 79 subjects with moderate to marked wrinkles, and instructed them to use both products, one on each side of the face, every morning for 12 weeks. The subjects didn't know which products they were using. At the end of the study, panelists examined before and after photos of the subjects to assess wrinkle appearance. The panelists did not know which product the subjects had used. Which of the following statements is TRUE?

A)This study is just anecdotal.
B)This study was an experiment, but not a double-blind experiment.
C)This study was a double-blind experiment, but not a randomized experiment.
D)This study was a randomized, double-blind experiment.

Question 37

A study examined the impact of THC (the active ingredient in marijuana) on various physiological and psychological variables. The study recruited a sample of 18 young adults who were habitual marijuana smokers. Participants came to the lab 3 times, each time completing the entire series of tests and questionnaire, but each time smoking a different marijuana cigarette: one with 3.9% THC, one with 1.8% THC, and one with no THC (a placebo). The order of the conditions was randomized and participants were not told how much THC was in the cigarette they smoked until after all the data were collected. This is an example of

A)anecdotal evidence.
B)a case-control observational study.
C)a completely randomized experiment.
D)a matched pairs or repeated measures experiment.

Question 38

What is the best description of an observed effect so large that it would rarely occur by chance?

A)Statistically impossible
B)Statistically significant
C)Does not imply causation
D)A mistake by the researcher

Question 39

Comparative design ensures that influences other than the experimental treatments operate equally on all groups.

Question 40

An excellent experimental design guarantees that any difference between two groups is entirely due to differences in the treatments applied.