Sampling and Experimental Design Practice Test
1.What do we call a sample that consists of the entire population?(a)A stratum(b)A multistage sample(c)A mistake. A sample can never be the entire population.(d)A census(e)None of the above. The answer is _________________________. 2.To test the effect of music on productivity, workers are observed. For one month background music is played. For another month, no music is played. This is an example of (a)an independent sample.(b)an observational study.(c)a completely randomized design.(d)a block design.(e)a paired sample.3.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)None of the above. The answer is _____________________________. 4.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)None of the above. The answer is _____________________________. 5.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)None of the above. The answer is ______________________________. 6.An experiment was designed to investigate the effect of the amount of water and seed variety upon subsequent growth of plants. Each plant was potted in a clay plot, and a measured amount of water was given weekly. The height of the plant at the end of the experiment was measured. Which of the following is not correct?(a) The response variable is the plant height.(b) The explanatory variables are the amount of water and seed variety.(c) Randomization was used to even out the effect of other possible factors upon the growth of the plants.(d) A possible uncontrollable factor in this experiment is any nutrients that might be present in the clay pots.(e) Designed experiments give the best evidence of “cause-and-effect” relationships.7. What electrical changes occur in muscles as they get tired? Student subjects 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.8. The Community Intervention Trial for Smoking Cessation (COMMIT) asked whether a community-wide advertising campaign would reduce smoking. The researchers located 11 pairs of communities that were similar in location, size, economic status, and so on. One community in each pair participated in the advertising campaign and the other did not. This is(a) an observational study.(b) a matched pairs experiment.(c) a completely randomized experiment.(d) a block design.(e) impossible to answer unless more details of the study are provided.9.Which of the following is CORRECT?(a) We do not need to randomize if our sample size is sufficiently large.(b) A large sample size always ensures that our sample is representative of the population.(c) If all other things are equal, we need a larger sample size for a larger population.(d) In a properly chosen sample, an estimate will be less variable with a large sample size and hence more precise.(e) In random samples, the randomization ensures that we get precise and accurate estimates.10.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 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 be dangerous 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.11. The following numbers appear in a table of random digits: 38683 50279 38224 09844 13578 28251 12708 24684A scientist will be measuring the total amount of woody debris in a random sample (n = 5) of sites selected without replacement from a population of 45 sites. The sites are labeled 01, 02, . . . , 45 and she starts at the beginning of the line of random digits and takes consecutive pairs of digits. Which of the following is correct?(a) Her sample is 38, 25, 02, 38, 22(b) Her sample is 38, 68, 35, 02, 22(c) Her sample is 38, 35, 27, 28, 08(d) Her sample is 38, 65, 35, 02, 79(e) Her sample is 38, 35, 02, 22, 4012.A committee on community relations in a college town plans to survey local businesses about the importance of students as customers. From telephone book listings, the committee chooses 150 businesses at random. Of these, 73 return the questionnaire mailed by the committee. The population for this study is(a) all businesses in the college town.(b) all businesses.(c) the 150 businesses chosen.(d) the 73 businesses that returned the questionnaire.(e) the committee on community relations.13. A new headache remedy was given to a group of 25 subjects who had headaches. Four hours after taking the new remedy, 20 of the subjects reported that their headaches had disappeared. From this information you conclude(a) that the remedy is effective for the treatment of headaches.(b) nothing, because the sample size is too small.(c) nothing, because there is no control group for comparison.(d) that the new treatment is better than aspirin.(e) that the remedy is not effective for the treatment of headaches.14.An experimenter wishes to test whether or not two types of fish food (a standard fish food and a new product) work equally well at producing fish of equal weight after a 2-month feeding program. The experimenter has 2 identical fish tanks (1 and 2) to put fish in and is considering how to assignthe 40 tagged fish to the tanks. To properly assign the fish, one step would be to(a)put all the odd tagged numbered fish in one tank, the even in the other, and give the standard food type to the odd numbered ones.(b) obtain pairs of fish whose weights are virtually equal at the start of the experiment and randomly assign one to tank 1 and the other to tank 2, with the feed assigned at random to the tanks.(c) proceed as in (b), but put the heavier of the pair into tank 2.(d) assign the fish at random to the two tanks and give the standard feed to tank 1.(e) not proceed as in (b) because using the initial weight in (b) is a nonrandom process. Use the initial length of the fish instead.15. A student wishes to examine the effect of wing width and wing length on the length of flight of a paper airplane. There are 4 different models of airplanes. Which of the following is NOT correct?(a) A factor (such as wing width) is an explanatory variable under control of the experimenter.(b) The order of flights was randomized to remove the influence of any other variables upon the flight distance of each flight.(c) It would be better to make four copies of each model of plane to give some feel for the plane-to-plane variations. (d) Flying each model four times would give information about the variation in flight length for each model.(e) Planned experiments (where randomization can take place) provide some of the strongest evidence in trying to establish a causal relationship.16 An experiment was conducted where you flew paper airplanes after modifying wing width and wing length. There were four different models of airplane. One design consideration was the choice between flying each plane four times or making four copies of each model, each of which is flown once. Which of the following is NOT correct?(a) Flying multiple copies of each model (that is, separate planes of each model) could give information on variability in flight due to fabrication effects (that is, how you made the plane).(b) Flying a single copy of each model four times could give information on variability in flight due to changes in initial launch conditions.(c) The differences in flight length among the different models give information on the “effects” of the design factors: wing width and wing length.(d) The response variable is flight length; the explanatory variables are wing width and wing lenght.(e) The net effect, whether flying each plane four times or flying four copies of each model once, would be the same.Free Response Section17.Suppose the Richmond-Times Dispatch asks a sample of 150 Richmonders their opinions on the quality of life in Richmond. (a)Is this study an experiment? Explain why or why not.(b)Identify the sample and the population in this study.50800340360Aspirin may enhance impairment by alcoholAspirin, a long time antidote for the side effects of drinking, may actually enhance alcohol’s effect, researchers at the Bronx Veterans’ Affairs Medical Center say. In a report on a study published in the Journal of the American Medical Association, the researchers said they found that aspirin significantly lowered the body’s ability to break down alcohol in the stomach. As a result, five volunteers who had a standard breakfast and two extra-strength aspirin tablets an hour before drinking had blood alcohol levels 30 percent higher than when they drank alcohol alone. Each volunteer consumed the equivalent of a glass and a half of wine. That 30 percent could make the difference between sobriety and impairment, said Dr. Charles S. Lieber, medical director of the Alcohol Research and Treatment Center at the Bronx center, who was co-author of the report with Dr. Risto Roine.00Aspirin may enhance impairment by alcoholAspirin, a long time antidote for the side effects of drinking, may actually enhance alcohol’s effect, researchers at the Bronx Veterans’ Affairs Medical Center say. In a report on a study published in the Journal of the American Medical Association, the researchers said they found that aspirin significantly lowered the body’s ability to break down alcohol in the stomach. As a result, five volunteers who had a standard breakfast and two extra-strength aspirin tablets an hour before drinking had blood alcohol levels 30 percent higher than when they drank alcohol alone. Each volunteer consumed the equivalent of a glass and a half of wine. That 30 percent could make the difference between sobriety and impairment, said Dr. Charles S. Lieber, medical director of the Alcohol Research and Treatment Center at the Bronx center, who was co-author of the report with Dr. Risto Roine.18.Read the following brief article about aspirin and alcohol.(a)Does this article describe an experiment or an observational study? Explain.(b)Did this study involve a simple random sample (SRS)? Explain.(c)Did this study use a particular design that we have studied? If so, identify the design. Then comment on the validity of the study.19.Bias is present in each of the following two sampling designs. In each case, identify the type of bias involved and state whether you think the sample result obtained is lower or higher than the actual population parameter.(a)A political pollster seeks information about the proportion of American adults who oppose gun controls. He asks an SRS of 1000 American adults: “Do you agree or disagree with the following statement: Americans should preserve their constitutional right to keep and bear arms.” A total of 910, or 91%, said, “Agree” (that is, 910 out of the 1000 oppose gun controls).(b)A flour company in Minneapolis wants to know what percent of local households bake at least twice a week. A company representative calls 500 households during the daytime and finds that 50% of them bake at least twice a week.20. High blood pressure adds to the workload of the heart and arteries and may increase the risk of heart attacks. If not treated, this condition can also lead to heart failure, kidney failure, or stroke. Angiotensin-converting enzyme (ACE) inhibitors are used to treat high blood pressure. It is well known that men and women may react differently to common cardiovascular drug treatments. Most studies of heart drugs involved only a very small percent of women, and it was simply assumed that the drug would work the same in both sexes. We want to conduct an experiment to see if ACE inhibitors are less effective in women than in men.(a)What sort of experimental design would you choose for this study, and why?(b)Assume that 600 men and 500 women suffering from high blood pressure are available for the study. Outline in a diagram the design of the experiment. Be sure to indicate how many subjects are assigned to the various treatment groups. (c)Use line 134 of the random digits table (below) to select the first 3 men for the study, and use line 142 to select the first 3 women for the study.134 27816 78416 18329 21337 35213 37741 04312 6850814272829 50232 97892 63408 77919 44575 24870 0417821.Do you trust the Internet? You want to ask a sample of college students the question “How much do you trust information about health that you find on the Internet—a great deal, somewhat, not much, or not at all?” You try out this and other questions on a pilot group of 10 students chosen from your class. The class members areAndersonDeng Glaus Nguyen SamuelsArroyo De RamosHelling Palmiero ShenBatista Drasin Husain Percival TseBell Eckstein Johnson Prince VelascoBurke FernandezKim Puri WallaceCabrera Fullmer Molina Richards WashburnCalloway Garcia Morgan Rider ZabidiDelluci Gandhi Murphy RodriguezZhaoChoose an SRS of 10 students. Use Table B, shown below, beginning at line 117. Explain your method clearly.11738167 98532 62183 70632 23417 26185 41448 7553211873190 32533 04470 29669 84407 90785 65956 8638211995857 07118 87664 92099 58806 66979 98624 84826 12035476 55972 39421 65850 04266 35435 43742 1193722. Canada requires that cars be equipped with “daytime running lights,” headlights that automatically come on at a low level when the car is started. Many manufacturers are now equipping cars sold in the United States with running lights. Will running lights reduce accidents by making cars more visible?(a) Describe the design of an experiment to help answer this question. In particular, what response variables will you examine? (b) What cautions do you see that might apply to an experiment on the effects of running lights?23. Does ginkgo improve memory? The law allows marketers of herbs and other natural substances to make health claims that are not supported by evidence. Brands of ginkgo extract claim to “improve memory and concentration.” A randomized comparative experiment found no evidence for such effects. The subjects were 230 healthy people over 60 years old. They were randomly assigned to ginkgo or a placebo pill (a dummy pill that looks and tastes the same). All the subjects took a battery of tests for learning and memory before treatment started and again after six weeks.(a)What are the explanatory and response variables in this experiment?(b)Outline the design of this experiment.(c)The study was double-blind. What does this mean? (d)Use Table B, starting at line 103 (below), and choose only the first 5 members of the ginkgo group.103 45467 71709 77558 00095 32863 29485 82226 90056104 52711 38889 93074 60227 40011 85848 48767 52573105 95592 94007 69971 91481 60779 53791 17297 59335106 68417 35013 15529 72765 85089 57067 50211 47487 ................
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