AP Stat Chapter 4

A study of cell phones and the risk of brain cancer looked at a group of 469 people who had brain cancer. The investigators matched each cancer patient with a person of the same sex, age, and race who did not have brain cancer, and then asked about their use of cell phones. This is : A) An observational study B) An uncontrolled experiment C) A randomized experiment D) A matched pairs experiment E) A survey

A

Do product labels influence customer perceptions? To find out, researchers recruited over 500 adults and asked them to estimate the number of calories, amount of added sugar, and amount of fat in a variety of food products. Half of the subjects were randomly assigned to evaluate products with the word "Natural" on the label while the other half were assigned to evaluate the same products without the "Natural" label. On average, the products with the "Natural" label were judged to have significantly fewer calories. Based on this study, it is reasonable to conclude that including the word "Natural" on the label causes a reduction in estimated calories? a) No, because the adults weren't randomly selected from the population of all adults. b) No, because there wasn't a control group for comparison. c) No, because association doesn't imply causation. d) Yes, because the adults were randomly assigned to the treatments. e) Yes, because there were a large number of adults involved in the study.

A

Which of the following are true about the design of matched-pair experiments? I. Each subject might receive both treatments II. Each pair of subjects receives the identical treatment, and differences in their responses are noted. III. Blocking is one form of matched-pair design a) I only b) II only c) III only d) I and III e) II and III

A

Which of the following is not required in an experimental design? A) blocking B) control C) randomization D) replication E) all are required in an experimental design

A

A large simple random sample of people aged nineteen to thirty living in the state of Colorado was surveyed to determine which of two MP3 players just developed by a new company was preferred. To which of the following populations can the results of this survey safely be generalized? A. Only people aged nineteen to thirty living in the state of Colorado who were in this survey. B. Only people aged nineteen to thirty living in the state of Colorado. C. All people living in the state of Colorado. D. Only people aged nineteen to thirty living in the United States. E. All people living in the United States.

B

Google and Gallup teamed up to survey a random sample of 1673 U.S. students in grades 7-12. One of the questions was "How confident are you that you could learn computer science if you wanted to?" Overall, 54% of students said they were very confident, with 62% of males and 48% of females saying they were very confident. Which of the three estimates (54%, 62%, 48%) do you expect is closest to the value it is trying to estimate? a) 48% b) 54% c) 62% d) All three estimates are equally precise e) There is not enough information to answer

B

Which of the following can be used to show a cause and effect relationship between two variables? A) a census B) a controlled experiment C) an observational study D) a sample survey E) a cross-sectional survey

B

Which of the following is the best description of a simple random sample of size n from a population of size N? (a) A sampling method in which individuals are selected in a completely haphazard fashion. (b) A sampling method in which every group of individuals of size n is equally likely to be selected. (c) A sampling method in which every individual is equally likely to be selected. (d) A sampling method in which each individual has a probability of n/N of being selected.

B

For the track coach's study described in the previous exercise, which of the following best describes a conclusion that can be drawn? (a) We can determine whether race times are faster for runners in the new program, but we can't establish cause and effect. (b) We can determine whether the new training program improves race times more than the standard program for any distance runner. (c) We can determine whether the new training program improves race times more than the standard program for distance runners like those in this study. (d) We cannot draw any conclusions, because all the volunteers were already members of this coach's team. (e) We cannot draw any conclusions, because there was no control group.

C

More dogs are being diagnosed with thyroid problems than have been diagnosed in the past. A researcher identified 50 puppies without thyroid problems and kept records of their diet for several years to see if any developed thyroid problems. This is a(n) a. randomized experiment b. survey c. prospective study d. retrospective study e. blocked experiment c. prospective study

C

Placebos are tools for A) sampling B) blocking C) blinding D) control E) randomization

C

A chemistry professor who teaches a large lecture class surveys his students who attend his class about how he can make the class more interesting, hoping he can get more students to attend. This survey method suffers from: A) Voluntary response bias B) Nonresponse bias C) Response bias D) Undercoverage E) None of the above

D

To check the effect of cold temperature on the elasticity of two brands of rubber bands, one box of Brand A and one box of Brand B rubber bands are tested. Ten bands from the Brand A box are placed in a freezer for two hours and ten bands from the Brand B box are kept at room temperture. The amount of stretch before breakage is measured on each rubber band, and the mean for the cold bands is compared to the mean for the others. Is this a good experimental design? A) No, because the means are not proper statistics for comparison B) No, because more than two brands should be used C) No, because more temperatures should be used D) No, because temperature is confounded with brand E) Yes

D

Consider the following studies being run by three different nursing home establishments. I.One nursing home has pets brought in for an hour every day to see if patient morale is improved. II.One nursing home allows hourly visits every day by kindergarten children to see if patient morale is improved. III.One nursing home administers antidepressants to all patients to see if patient morale is improved. Which of the following is true? A. None of these studies uses randomization. B. None of these studies uses control groups. C. None of these studies uses blinding. D. Important information can be obtained from all these studies, but none will be able to establish causal relationships. E. All of the above

E

In a recent poll of 1,500 randomly selected eligible voters, only 525 (35 percent) said that they did not vote in the last election. However, a vote count showed that 80 percent of eligible voters actually did not vote in the last election. Which of the following types of bias is most likely to have occurred in the poll? A) Nonresponse bias B) Sampling bias C) Selection bias D) Response bias E) Undercoverage bias

D

Control groups are used in experiments in order to accomplish which one of the following? (a) Limit the effects of variables other than the explanatory variable on the outcome. (b) Control the subjects of a study to ensure that all participate equally. (c) Guarantee that someone other than the investigators, who have a vested interest in the outcome, controls how the experiment is conducted. (d) Achieve a proper and uniform level of randomization. (e) Reduce variability in results.

A

A maple sugar manufacturer wants to estimate the average trunk diameter of Sugar Maples trees in a large forest. There are too many trees to list them all and take a SRS, so he divids the forest into several hundred 10 meter by 10 meter plots, selects 25 plots at random, and measures the diameter of every Sugar Maple in each one. This is an example of a (a) multistage sample. (b) stratified sample. (c) simple random sample. (d) cluster sample. (e) convenience sample.

D

Which of the following is a key distinction between well designed experiments and observational studies? (A) More subjects are available for experiments than for observational studies. (B) Ethical constraints prevent large-scale observational studies. (C) Experiments are less costly to conduct than observational studies. (D) An experiment can show a direct cause-and-effect relationship, whereas an observational study cannot. (E) Tests of significance cannot be used on data collected from an observational study

D

In the design of a survey, which of the following best explains how to minimize response bias? A. Increase sample size. B. Decrease sample size. C. Randomly select the sample. D. Increase the number of questions in the survey. E. Carefully word and field-test survey questions.

E

A newspaper editor wants to investigate whether residents of the city support a proposal to build a new high school football stadium. The editor hires a polling firm to conduct a survey and requests that a sample of 500 residents be selected using a stratified sampling design based on voting districts within the city. Which of the following methods will achieve the desired sampling design? (A) Send a survey to all city residents and use the first 500 returned surveys for the sample. (B) Select a random sample from each voting district based on the proportion of city residents in the district so that a total of 500 is obtained. (C) Select one voting district at random, and then select a random sample of 500 from the selected voting district. (D) Alphabetize a list of all city residents, and then select the first 500 residents on the list, classifying those selected by voting district. (E) Select the first 500 city residents who attend the next high school football game.

B

Researchers working for a certain airline are investigating the weight of carry-on bags. The researchers will use the mean weight of a random sample of 1,300 carry-on bags to estimate the mean weight of all carry-on bags for the airline. Which of the following best describes the effect on the bias and the variance of the estimator if the researchers increase the sample size to 800? a. The bias will decrease and the variance will remain the same. b. The bias will increase and the variance will remain the same. c. The bias will remain the same and the variance will decrease. d. The bias will remain the same and the variance will increase. e. The bias will decrease and the variance will decrease.

C

We say that the design of a study is biased if (a) the sample isn't perfectly representative of the population. (b) you get a sample result that differs from the true value. (c) it is very likely to underestimate or very likely to overestimate the value you want to know. (d) the correlation is greater than 1 or less than -1. (e) an observational study was used when an experiment would have been feasible.

C

We say that the design of a study is biased if which of the following is true? (a) A racial or sexual preference is suspected. (b) Random placebos have been used. (c) Certain outcomes are systematically favored. (d) The correlation is greater than 1 or less than -1. (e) An observational study was used when an experiment would have been feasible.

C

Which of the following are true statements about sampling error? I. Sampling error can be eliminated only if a survey is both extremely well designed and extremely well conducted. II. Sampling error concerns natural variation between samples, is always present, and can be described using probability. III. Sampling error is generally smaller when the sample size is larger. a) I and II b) I and III c) II and III d) I, II, and III e) None of the above

C

A new medication has been developed to treat sleep-onset insomnia (difficulty in falling asleep). Researchers want to compare this drug to a drug that has been used in the past by comparing the length of time it takes subjects to fall asleep. Of the following, which is the best method for obtaining this information? (A) Have subjects choose which drug they are willing to use, then compare the results. (B) Assign the two drugs to the subjects on the basis of their past sleep history without randomization, then compare the results. (C) Give the new drug to all subjects on the first night. Give the old drug to all subjects on the second night. Compare the results. (D) Randomly assign the subjects to two groups, giving the new drug to one group and no drug to the other group, and then compare the results. (E) Randomly assign the subjects to two groups, giving the new drug to one group and the old drug to the other group, and then compare the results.

E

A new restaurant is interested in determining the best time-temperature combination for roasting a five-pound cut of lamb. The times to be tested are 45 minutes, 60 minutes, and 90 minutes at temperatures of 350 degrees Fahrenheit and 425 degrees Fahrenheit for each time, with the exception of the 90 minute-425 degree combination. That combination is being eliminated because it will overcook the lamb, which leaves five combinations remaining. From 10 identical cuts of lamb, 2 are randomly selected to roast using each of the time-temperature combinations in the same oven. The quality of the finished product is evaluated for each roast. Which of the following is true? A) The explanatory variable is the quality of the finished lamb B) The response variable is the roasting temperature for the lamb C) If the experiment is repeated, identical results will be expected D) There should be a control group (i.e., a group in which no treatment is given) E) The two cuts that are being roasted for each time-temperature combination are an example of replication

E

The buyer for an electronics store wants to estimate the proportion of defective wireless game controllers in a shipment of 5,000 controllers from the store's primary supplier. The shipment consists of 200 boxes each containing 25 controllers. The buyer numbers the boxes from 1 to 200 and randomly selects six numbers in that range. She then opens the six boxes with the corresponding numbers, examines all 25 controllers in each of these boxes, and determines the proportion of the 150 controllers that are defective. What type of sample is this? A) Biased random sample B) Nonrandom sample C) Simple random sample D) Stratified random sample E) Cluster random sample

E

Automobile brake pads are either metallic or nonmetallic. An experiment is to be conducted to determine whether the stopping distance is the same for both types of brake pads. In previous studies, it was determined that car size (small, medium, large) is associated with stopping distance, but car type (sedan, wagon, coupe) is not associated with stopping distance. The experiment would be best done (A) by blocking on car size (B) by blocking on car type (C) by blocking on stopping distance (D) by blocking on brake pad type (E) without blocking

A

Below is a dotplot of the percentage of made free throws by a 60% free-throw shooter in 100 computer simulations of 16 free throws. Brayden was a 60% free throw shooter last season. He practiced all through the off-season and has made 12 of the first 16 free throws this season. Based on his performance and the results of the simulation, is there convincing evidence that Brayden has improved his free-throw percentage? Explain. (a) No. The simulation shows that there is a 14% chance of doing that well or better even if he is still a 60% free throw shooter. (b) No. The simulation shows that there is a 9% chance of doing that well or better even if he is still a 60% free throw shooter. (c) Yes. The simulation shows that there is a 14% chance of doing that well or better even if he is still a 60% free throw shooter. (d) Yes. The simulation shows that there is a 9% chance of doing that well or better even if he is still a 60% free throw shooter. (e) Yes. He made 12/16 = 75% of his free throws, which is more than 60%. This proves that he has improved.

A

Control groups are used in experiments in order to (a) control the effects of outside variables on the outcome. (b) control the subjects of a study to ensure that all participate equally. (c) guarantee that someone other than the investigators, who have a vested interest in the outcome, controls how the experiment is conducted. (d) achieve a proper and uniform level of randomization. (e) reduce the variability in results.

A

Many utility companies have introduced programs to encourage energy conservation among their customers. An electric company considers placing small digital displays in households to show current electricity use and what the cost would be if this use continued for a month. Will the displays reduce electricity use? One cheaper approach is to give customers a chart and information about monitoring their electricity use from their outside meter. Would this method work almost as well? The company decides to conduct an experiment to compare these two approaches (display, chart) with a group of customers who receive information about energy consumption but no help in monitoring electricity use. 60 single-family residences volunteer to take part in this study and each residence is randomly assigned to one of the treatments. An electric company in a different city decides to conduct a similar experiment, but wants to use a blocked design. Which of the following variables would be the least useful blocking variable? a) Color of the residence b) Previous month's electricity bill c) Size of house, in square feet d) Number of people that live in the residence e) Whether or not the residence has an air conditioner

A

Many utility companies have introduced programs to encourage energy conservation among their customers. An electric company considers placing small digital displays in households to show current electricity use and what the cost would be if this use continued for a month. Will the displays reduce electricity use? One cheaper approach is to give customers a chart and information about monitoring their electricity use from their outside meter. Would this method work almost as well? The company decides to conduct an experiment to compare these two approaches (display, chart) with a group of customers who receive information about energy consumption but no help in monitoring electricity use. 60 single-family residences volunteer to take part in this study and each residence is randomly assigned to one of the treatments. What is the purpose of randomly assigning the residences to treatments? a) Random assignment allows the company to generalize the results to all customers. b) To prevent non-response among the 60 residences that volunteer. c) To make sure that the study is double-blind. d) To create groups of residences that are roughly equivalent at the beginning of the study. e) To reduce the variability in electricity use among the three groups.

A

Which of the following are true statements? I. Based on careful use of control groups, experiments can often indicate cause-and-effect relationships. II. While observational studies may suggest relationships, great care must be taken in concluding that there is cause and effect because of the lack of control over lurking variables. III. A complete census is the only way to establish a cause-and-effect relationship absolutely. (A) I and II (B) I and III (C) II and III (D) I, II, and III (E) None of the above gives the complete set of true responses.

A

a dog food company wishes to test a new high protein formula for puppy food to determine whether it promotes faster wait gain than the existing formula for that puppy food. puppies participating in an experiment will be weighed at waning and will be weighed at one month intervals for on year. in designing this experiment the investigators wish to reduce the variability due to natural differences in puppy growth rates. which of the following strategies is most appropriate for accomplishing this? A) Block on dog breed and randomly assign puppies to existing and new formula groups within each breed B) Block on geographic location and randomly assign puppies to existing and new formula groups within each geographic area C) Stratify on dog breed and randomly sample puppies within each breed. Then assign puppies by breed to either the existing or the new formula D) Stratify on geographic location of the puppies and randomly sample puppies within each geographic area. Then assign puppies by geographic area to either the existing or new formula. E) Stratify on gender and randomly sample puppies within gender groups. Then assign puppies by gender to either the existing or the new formula.

A

A polling firm is interested in surveying a representative sample of registered voters in the United States. The firm has automated its Bsampling so that random phone numbers within the United States are called. Each time a number is called, the procedure below is followed. • If there is no response or if an answering machine is reached, another number is automatically called. • If a person answers, a survey worker verifies that the person is at least 18 years of age. • If the person is not at least 18 years of age, no response is recorded, and another number is called. • If the person is at least 18 years of age, that person is surveyed. Some people claim the procedure being used does not permit the results to be extended to all registered voters. Which of the following is NOT a legitimate concern about the procedure being used? A) Registered voters with children under the age of 18 years may be underrepresented in the sample. B) Registered voters with unlisted telephone numbers may be underrepresented in the sample. C) Registered voters who have more than one telephone number may be overrepresented in the sample. D) Registered voters who live in households consisting of more than one voter may be underrepresented. E) People who are not registered to vote may bias the sample results.

B

A researcher wants to compare the effect of a new type of shampoo on hair condition. The researcher believes that men and women may react to the shampoo differently. Additionally, the researcher believes that the shampoo will react differently on hair that is dyed. The subjects are split into four groups: men who dye their hair; men who do not dye their hair, women who dye their hair; women who do not dye their hair. Subjects in each group are randomly assigned to the new shampoo and the old shampoo. This experiment: A) is completely randomized. B) has one factor (shampoo type), blocked by gender and whether hair is dyed. C) has three factors (shampoo type, gender, whether hair is dyed). D) has two factors (gender and whether hair is dyed) blocked by shampoo type. E) has two factors (shampoo type and whether hair is dyed) blocked by gender.

B

A researcher wishes to test a new drug developed to treat hypertension (high blood pressure). A group of 40 hypertensive men and 60 hypertensive women is to be used. The experimenter randomly assigns 20 of the men and 30 of the women to the placebo and assigns the rest to the treatment. The major reason for separate assignment for men and women is that (A) it is a large study with 100 subjects (B) the new drug may affect men and women differently (C) the new drug may affect hypertensive and nonhypertensive people differently (D) this design uses matched pairs to detect the new-drug effect (E) there must be an equal number of subjects in both the placebo group and the treatment group.

B

A television news editor would like to know how local registered voters would respond to the question, "Are you in favor of the school bond measure that will be voted on in an upcoming special election?" A television survey is conducted during a break in the evening news by listing two telephone numbers side by side on the screen, one for viewers to call if they approve of the bond measure, and the other to call if they disapprove. This survey method could produce biased results for a number of reasons. Which one of the following is the most obvious reason? (A) It uses a stratified sample rather than a simple random sample. (B) People who feel strongly about the issue are more likely to respond. (C) Viewers should be told about the issues before the survey is conducted. (D) Some registered voters who call might not vote in the election. (E) The wording of the question is biased.

B

Consider an experiment to investigate the effectiveness of different insecticides in controlling pests and their impact on the productivity of tomato plants. What is the best reason for randomly assigning treatment levels (spraying or not spraying) to the experimental units (farms)? (a) Random assignment allows researchers to generalize conclusions about the effectiveness of the insecticides to all farms. (b) Random assignment will tend to average out all other uncontrolled factors such as soil fertility so that they are not confounded with the treatment effects. (c) Random assignment eliminates the effects of other variables, like soil fertility. (d) Random assignment eliminates chance variation in the responses. (e) Random assignment helps avoid bias due to the placebo effect.

B

Eighty volunteers who currently use a certain brand of over-the-counter allergy medication have been recruited to participate in a trial of a new allergy medication. The volunteers are randomly assigned to one of two groups. One group continues to take their current medication, the other group switches to the new experimental medication. Each is asked after two weeks if their allergy symptoms are worse, better, or about the same as they were at the start of the study. Which of the follow best describes a conclusion that can be drawn from this study? (a) We can determine whether the new drug reduces symptoms more than the old drug for anyone who suffers from allergies. (b) We can determine whether the new drug reduces symptoms more than the old drug for the subjects in the study. (c) We can determine whether the allergies sufferers' symptoms improved more with the new drug than with the old drug, but we can't establish cause and effect. (d) We cannot draw any conclusions, since the all the volunteers were already taking the old drug when the experiment started. (e) We cannot draw any conclusions, because there was no control group.

B

Select the best answer. A researcher wishes to compare the effects of two fertilizers on the yield of soybeans. She has 20 plots of land available for the experiment, and she decides to use a matched pairs design with 10 pairs of plots. To carry out the random assignment for this design, the researcher should (a) use a table of random numbers to divide the 20 plots into 10 pairs and then, for each pair, flip a coin to assign the fertilizers to the 2 plots. (b) subjectively divide the 20 plots into 10 pairs (making the plots within a pair as similar as possible) and then, for each pair, flip a coin to assign the fertilizers to the 2 plots. (c) use a table of random numbers to divide the 20 plots into 10 pairs and then use the table of random numbers a second time to decide on the fertilizer to be applied to each member of the pair. (d) flip a coin to divide the 20 plots into 10 pairs and then, for each pair, use a table of random numbers to assign the fertilizers to the 2 plots. (e) use a table of random numbers to assign the two fertilizers to the 20 plots and then use the table of random numbers a second time to place the plots into 10 pairs.

B

Some news organizations maintain a database of customers who have volunteered to share their opinions on a variety of issues. Suppose that one of these databases includes 9000 registered voters in California. To measure the amount of support for a controversial ballot issue, 1000 registered voters in California are randomly selected from the database. Which of the following is the largest population to which the results of this survey should be generalized? a) The 1000 people in the sample. b) The 9000 registered voters from California in the database. c) All registered voters in California. d) All California residents. e) All registered voters in the United States.

B

To test the effects of a new fertilizer, 100 plots were divided in half. Fertilizer A is randomly applied to one half, and B to the other. This is (a) an observational study. (b) a matched pairs experiment. (c) a completely randomized experiment. (d) a block design, but not a matched pairs experiment. (e) impossible to classify unless more details of the study are provided.

B

What electrical changes occur in muscles as they get tired? Student subjects are instructed to hold their arms above their shoulders as long as they can. Meanwhile, the electrical activity in their arm muscles is measured. This is (a) an observational study. (b) an uncontrolled experiment. (c) a randomized comparative experiment. (d) a matched pairs design. (e) impossible to describe unless more details of the study are provided.

B

What is the primary benefit of a stratified random sampling method compared to a simple random sample? a) It gives less biased results than a simple random sample. b) It gives more precise estimates than a simple random sample. c) It is easier to carry out than a simple random sample. d) It gives more variable estimates than a simple random sample. e) It allows cause-and-effect conclusions.

B

4. A survey is to be undertaken of recent nursing graduates in order to compare the starting salaries of women and men. For each graduate, three variables are to be recorded (among others) sex, starting salary, and area of specialization. (a) Sex and starting salary are explanatory variables; area of specialization is a response variable. (b) Sex is an explanatory variable; starting salary and area of specialization are response variables. (c) Sex is an explanatory variable; starting salary is a response variable; area of specialization is a possible confounding variable. (d) Sex is a response variable; starting salary is an explanatory variable; area of specialization is a possible confounding variable. (e) Sex and area of specialization are response variables; starting salary is an explanatory variable.

C

A track coach wants to test the effectiveness of a new training program for distance runners. He selects his two fastest runners and, using a coin flip, randomly chooses one to participate in the new program. The other will continue with the standard training regimen. He then picks the next two fastest runners and randomly assigns one to each program. He repeats this process with all his runners, choosing the two fastest remaining each time. He then compares race times within each group of two runners. This study uses which of the following? (a) A completely randomized design (b) A randomized block design, but not matched pairs (c) A matched pairs design (d) Cluster sampling (e) Stratified random sampling

C

An experiment to measure the effect of giving growth hormones to girls affected by Turner's Syndrome was carried out recently in Vancouver. All 34 girls in the study were given the growth hormone and their heights were measured at the time the hormone was given and again one year later. No measurements were made on their final adult heights. Which of the following is not a problem with this experiment: (a) There was no blinding. (b) There was no control group. (c) Nonresponse bias (d) There was insufficient attention to the placebo effect. (e) Because final heights were not measured, it is impossible to tell if the hormone affected final height or only accelerated growth and made no difference to final height.

C

Many utility companies have introduced programs to encourage energy conservation among their customers. An electric company considers placing small digital displays in households to show current electricity use and what the cost would be if this use continued for a month. Will the displays reduce electricity use? One cheaper approach is to give customers a chart and information about monitoring their electricity use from their outside meter. Would this method work almost as well? The company decides to conduct an experiment to compare these two approaches (display, chart) with a group of customers who receive information about energy consumption but no help in monitoring electricity use. 60 single-family residences volunteer to take part in this study and each residence is randomly assigned to one of the treatments. Which of the following lists the number of factors, number of treatments, and number of experimental units (in this order)? a) 3, 1, 60 b) 3, 1, 20 c) 1, 3, 60 d) 1, 3, 20 e) 3, 3, 60

C

Many utility companies have introduced programs to encourage energy conservation among their customers. An electric company considers placing small digital displays in households to show current electricity use and what the cost would be if this use continued for a month. Will the displays reduce electricity use? One cheaper approach is to give customers a chart and information about monitoring their electricity use from their outside meter. Would this method work almost as well? The company decides to conduct an experiment to compare these two approaches (display, chart) with a group of customers who receive information about energy consumption but no help in monitoring electricity use. 60 single-family residences volunteer to take part in this study and each residence is randomly assigned to one of the treatments. Why was it important to include a control group that received only information about energy consumption, but no help in monitoring electricity use? a) So the experiment would include replication. b) So the experiment could be done using a matched pairs design. c) Because all experiments require a control group. d) Because the 60 residences weren't randomly selected. e) So there is no confounding with changes in the weather.

C

Publishers of a magazine wish to determine what proportion of the magazine's 50,000 subscribers are pleased with their subscription. The publishers intend to mail a survey to 1,000 subscribers randomly selected from those who have received the magazine for 5 years or more. This introduces selection bias since long-subscribing customers are more likely to be pleased with their subscription. Which of the following would best eliminate selection bias? A. Mail surveys to 2,000 subscribers randomly selected from those who have received the magazine for 5 years or more. B. Mail survey to 1,000 subscribers randomly selected from those who have received the magazine for 1 year or less. C. Mail surveys to 1,000 subscribers randomly selected from all subscribers. D. Mail surveys to 1,000 subscribers randomly selected from those who have received the magazine for 5 years or more and 1,000 subscribers randomly selected from those who have received the magazine for 1 year or less. E. Mail surveys to 500 subscribers randomly selected from a group who have received a free six-month subscription within the past year.

C

Which of the following are true statements? I. Voluntary response samples often underrepresent people with strong opinions. II. Convenience samples often lead to undercoverage bias. III. Questionnaires with nonneutral wording are likely to have response bias. (A) I and II (B) I and III (C) II and III (D) I, II, and III (E) None of the above gives the complete set of true responses.

C

Which of the following is a method for improving the accuracy of a sample? (a) Use no more than 3 or 4 words in any question. (b) When possible, avoid the use of human interviewers, relying on computerized dialing instead. (c) Use large sample sizes. (d) Use smaller sample sizes. (e) Ask only questions for which the responses are quantitative variables.

C

A group of students has 60 houseflies in a large container and needs to assign 20 to each of the three groups labeled A, B, and C for an experiment. They can capture the flies one at a time when the flies enter a side chamber in the container that is baited with food. Which of the following methods will be most likely to result in three comparable groups of 20 houseflies each? (A) Label the first 20 flies caught as Group A, the second 20 caught as group B, and the third 20 caught as group C. (B) Write the letters A, B, and C on separate slips of paper. Randomly pick one of the slips of paper and assign the first 20 flies caught to that group. Pick another slip and assign the next 20 flies caught to that group. Assign the remaining flies to the remaining group. (C) When each fly is caught, roll a die. If the die shows an even number, the fly is labeled A. If the die shows an odd number, the fly is labeled B. When 20 flies have been labeled A and 20 have been labeled B, the remaining flies are then labeled C. (D) Place each fly in its own numbered container (numbered from 1 to 60) in the order that it was caught. Write the numbers from 1 to 60 on slips of paper, put the slips in a jar, and mix them well. Pick 20 numbers out of the jar. Assign the flies in the containers with those numbers to group A. Pick 20 more numbers and assign the flies in the containers with those numbers to group B. Assign the remaining 20 flies to group C. (E) When each fly is caught, roll a die. If the die shows a 1 or 2, the fly is labeled A. If the die shows a 3 or 4, the fly is labeled B. If the die shows a 5 or 6, the fly is labeled C. Repeat this process for all 60 flies.

D

A materials engineer wishes to compare the durability of two different types of paving material. She has 40 different one-mile stretches of interstate highway that she's been authorized to repave for this study. She decides to carry out a matched pairs experiment. Which of the following is the best way for her to carry out the randomization for this study? (a) Use a table of random digits to divide the 40 roadways into 20 pairs and then, for each pair, flip a coin to decide which pavement to use on which member of the pair. (b) Subjectively divide the 40 roadways into 20 pairs (making the roadways within each pair as different as possible) and then, for each pair, flip a coin to decide which pavement to use on which member of the pair. (c) Use a table of random digits to divide the 40 roadways into two groups of twenty, and then use the table of random digits a second time to decide which pavement to use on which group. (d) Let each of the 40 roadways act as its own pair, dividing each roadway into the first halfmile and the second half-mile. Flip a coin for each of the 40 roadways to decide which half-mile gets which pavement. (e) Let each of the 40 roadways act as its own pair, dividing each roadway into the first halfmile and the second half-mile. Flip a coin once to decide which pavement is put on the first half-mile of all the roadways.

D

A nutritionist wants to study the effect of storage time (6, 12, and 18 months) on the amount of vitamin C present in freeze dried fruit when stored for these lengths of time. Six fruit packs were randomly assigned to each of the three storage times. The treatment, experimental unit, and response are respectively: (a) A specific storage time, amount of vitamin C, a fruit pack (b) A fruit pack, amount of vitamin C, a specific storage time (c) Random assignment, a fruit pack, amount of vitamin C (d) A specific storage time, a fruit pack, amount of vitamin C (e) A specific storage time, six fruit packs, amount of vitamin C

D

A political action committee sends out a questionnaire to randomly-selected mailing addresses, asking people to rate the importance of a variety of economic and social issues facing the country. At the end of the questionnaire is an (optional) invitation to donate money to the political action committee. Which of the following statements about this survey is true? (a) The survey results are invalid because it's impossible to word questions about politics without creating bias. (b) The survey results are invalid because only surveys conducted by phone are free from bias. (c) The survey results will underestimate support for this political action committee in the entire population because people who respond are less likely to support an organization that asks for money. (d) The survey results will overestimate support for this political action committee in the entire population because people are more likely to respond if they are prepared to donate money. (e) Because the survey was sent to randomly-selected households, it should be free of bias.

D

A researcher planning a survey of heads of households in a particular state has census lists for each of the 23 counties in that state. The procedure will be to obtain a random sample of heads of households from each of the counties rather than grouping all the census lists together and obtaining a sample from the entire group. Which of the following is a true statement about the resulting stratified sample? I. It is not a simple random sample. II. It is easier and less costly to obtain than a simple random sample. III. It gives comparative information that a simple random sample wouldn't give. (A) I only (B) I and II (C) I and III (D) I, II, and III (E) None of the above gives the complete set of true responses

D

A study of existing records of 27,000 automobile accidents involving children in Michigan found that about 10 percent of children who were wearing a seatbelt (group SB) were injured and that about 15 percent of children who were not wearing a seatbelt (group NSB) were injured. Which of the following statements should NOT be included in a summary report about this study? (A) Driver behavior may be a potential confounding factor. (B) The child's location in the car may be a potential confounding factor. (C) This study was not an experiment, and cause-and-effect inferences are not warranted. (D) This study demonstrates clearly that seat belts save children from injury. (E) Concluding that seatbelts save children from injury is risky, at least until the study is independently replicated.

D

A survey is to be administered to recent graduates of a certain nursing school in order to compare the starting salaries of women and men. For a random sample of graduates, three variables are to be recorded: sex, starting salary, and area of specialization. Which of the follow best describes a conclusion that can be drawn from this study? (a) Whether being female causes graduates of this nursing school to have lower (or higher) starting salaries than males. (b) Whether being female causes graduates in this sample to have lower (or higher) starting salaries than males. (c) Whether choosing certain area of specialization causes females graduates of this nursing school to have lower (or higher) starting salaries than males. (d) Whether there is an association between sex and starting salary among graduates of this nursing school. (e) Whether there is an association between sex and starting salary at all nursing schools similar to this one.

D

A survey was done in the town of Mechanicsville to estimate the proportion of cars that are red and made by companies based in Japan. A simple random sample of 25 cars from a parking lot at Lee- Davis High School was taken. Which of the following statements is correct? (a) Since this is a simple random sample, it should be representative of all the cars in Mechanicsville. (b) If a simple random sample of 15 cars were taken, we would expect the same amount of variability in the proportion of red cars as we would with a sample of 25 cars. (c) An alternative method for getting a representative sample would be to select the 25 cars closest to a specified location, such as the entrance to the gymnasium. (d) A different team doing the sampling independently would probably obtain a slightly different answer for their sample proportion. (e) The results would be the same regardless of the time of day that the sample is taken.

D

An apartment complex is made up of 10 buildings with 12 apartments in each building. The manager wants to select a sample of apartments to gauge interest in a proposed improvements to the swimming pool. If the manager selects 20 apartments by randomly selecting 2 apartments from each building, what kind of sample did the manager obtain? a) Convenience sample b) Voluntary response sample c) Simple random sample d) Stratified random sample e) Cluster sample

D

An article in the student newspaper of a large university had the headline ―A's swapped for evaluations?‖ The article included the following. According to a new study, teachers may be more inclined to give higher grades to students, hoping to gain favor with the university administrators who grant tenure. The study examined the average grade and teaching evaluation in a large number of courses in order to investigate the effects of grade inflation on evaluations. ―I am concerned with student evaluations because instruction has become a popularity contest for some teachers,‖ said Professor Smith, who recently completed the study. Results showed that higher grades directly corresponded to a more positive evaluation. Which of the following would be a valid conclusion to draw from the study? (a) A teacher can improve his or her teaching evaluations by giving good grades. (b) A good teacher, as measured by teaching evaluations, helps students learn better, resulting in higher grades. (c) Teachers of courses in which the mean grade is above average apparently tend to have above-average teaching evaluations. (d) Teaching evaluations should be conducted before grades are awarded. (e) All of the above.

D

Suppose that Google and Gallup conducted their survey by placing ads on Google search results that said "Do you enjoy computer science? Click here to take a survey and possibly win a $100 gift card." If they receive 10,387 responses to the survey and find that 73% would agree with the question in #10, what do you conclude about all U.S. 7-12 graders? a) 73% is closer to the truth than 54% because the sample size is larger. b) 73% is closer to the truth than 54% because the survey was done online. c) 54% is closer to the truth than 73% because the sample size is smaller. d) 54% is closer to the truth than 73% because the sample was randomly selected. e) The truth must be somewhere between 54% and 73%.

D

We wish to investigate if a new medicine is effective in reducing the length and severity of the flu. We take the next 20 patience who come to the walk-in clinic complaining of flu and, after a medical exam to verify that the patience do have the flu, give them the new medicine and tell them about the new drug we are giving them. One week later, the patience are contacted and 15 patients state the new remedy was helpful in reducing the severity and length of the illness. Which of the following is not correct? A) This is a poor experiment as there is no control group B) This is a poor experiment because it is not double-blinded C) This is a poor experiment because a convenience sample was selected D) This is a poor experiment because we didn't give the remedy to people without the flu to assess its effect in a control group E) This is a poor experiment because the sample size is likely to be too small to detect anything but a large improvement when measuring the proportion to people reporting an improvement

D

Which of the following are true statements? I. In an experiment some treatment is intentionally administered to one group to note the response. II. In an observational study information is gathered on an already existing situation. III. Sample surveys are observational studies, not experiments. A) I and II B) I and III C) II and III D) I, II, and III E) None of the above

D

A survey was done in the town of Mechanicsville to estimate the proportion of cars that are red and made by companies based in Japan. A random sample of 25 cars from a student parking lot at Lee-Davis High School was taken. Which of the following statements is not correct? (a) This sample may not be representative of the cars in Mechanicsville because mainly students park at Lee-Davis High School. (b) If the particular parking space is vacant, we can simply select another parking space at random because it is unlikely that a space being vacant is related to the color or manufacturer of the car. (c) It would an error to simply select the first 25 parking spaces in the lot closest to the auditorium because there are a number of parking spaces there reserved for Drivers Ed vehicles, whose primary color is white. (d) A different team doing the sampling independently would obtain different answers for their sample proportions. (e) The results will be the same regardless of the time of day that the sample is taken.

E

In which of the following situations would it be most difficult to use a census? (A) To determine what proportion of licensed bicycles on a university campus have lights (B) To determine what proportion of students in a high school support wearing uniforms (C) To determine what proportion of registered students enrolled in a college are employed more than20 hours each week (D) To determine what proportion of single-family dwellings in a small town have two-car garages (E) To determine what proportion of fish in Lake Michigan are bass

E

The Physicians' Health Study, a large medical experiment involving 22,000 male physicians, attempted to determine whether aspirin could help prevent heart attacks. In this study, one group of about 11,000 physicians took an aspirin every other day, while a control group took a placebo. After several years, it was determined that the physicians in the group that took aspirin had significantly fewer heart attacks than the physicians in the control group. Which of the following statements explains why it would not be appropriate to say that everyone should take an aspirin every other day? I. The study included only physicians, and different results may occur in individuals in other occupations. II. The study included only males and there may be different results for females. III. Although taking aspirin may be helpful in preventing heart attacks, it may be harmful to some other aspects of health. A) I only B) II only C) III only D) II and III only E) I, II, and III

E

Which of the following is NOT a characteristic of stratified random sampling? (A) Random sampling is part of the sampling procedure. (B) The population is divided into groups of units that are similar on some characteristic. (C) The strata are based on facts known before the sample is selected. (D) Each individual unit in the population belongs to one and only one of the strata. (E) Every possible subset of the population, of the desired sample size, has an equal chance of being selected.

E

Which of the following statements is false? (a) Nonresponse can cause bias in surveys because nonrespondents often tend to behave differently than people who respond. (b) Non-sampling errors can distort the results of a census. (c) Slight changes in the wording of questions can make a measurable difference in survey results. (d) People will sometimes answer a question differently for different interviewers. (e) Sophisticated statistical methods can always correct the results if the population you are sampling from is different from the population of interest, for example, due to undercoverage.

E