1. Chapter 4
Potpourri

2. Surveys vs Experiments

3. Surveys vs Experiments

4. Surveys vs Experiments

5. Surveys vs Experiments

6. Surveys vs Experiments

7. Surveys vs Experiments

8. Surveys vs Experiments

9. Surveys vs Experiments

10. Surveys vs Experiments
Eliminates selection bias

11. Surveys vs Experiments

12. Surveys vs Experiments

13. Surveys vs Experiments

14. Surveys vs Experiments

15. Surveys vs Experiments

16. Surveys vs Experiments

17. Surveys vs Experiments

18. Surveys vs Experiments

19. Sampling
1. What is the difference between the groups for cluster sampling and stratified random sampling?

20. Sampling
What is the difference between the groups for cluster sampling and stratified random sampling?
Clusters: similar characteristics; each group is representative of population
Stratified: different characteristics
--level of income, political party

21. 2. What is the key to reducing confounding in an experiment?

22. 2. What is the key to reducing confounding in an experiment?
Assign treatments at random to experimental units

23. 3. Suppose pairs of identical twins agree to participate in an experiment to test the effect of salt on blood pressure. It is decided by a coin flip which of the twins will consume a high-salt diet and which will consume a low-salt diet. The response variable will be their blood pressure after ten weeks on the diet. This is an example of ___________.

24. 3. Suppose pairs of identical twins agree to participate in an experiment to test the effect of salt on blood pressure. It is decided by a coin flip which of the twins will consume a high-salt diet and which will consume a low-salt diet. The response variable will be their blood pressure after ten weeks on the diet. This is an example of
A. a completely randomized design
B. a randomized paired comparison design (matched pairs)
C. a randomized paired comparison design with repeated measures on the same subject
D. stratification
E. two-stage cluster sampling

25. 3. Suppose pairs of identical twins agree to participate in an experiment to test the effect of salt on blood pressure. It is decided by a coin flip which of the twins will consume a high-salt diet and which will consume a low-salt diet. The response variable will be their blood pressure after ten weeks on the diet. This is an example of
A. a completely randomized design
B. a randomized paired comparison design (matched pairs)
C. a randomized paired comparison design with repeated measures on the same subject
D. stratification
E. two-stage cluster sampling

26. 4. When the effects of two variables on a response variable cannot be distinguished from each other, the variables are said to be __________.

27. 4. When the effects of two variables on a response variable cannot be distinguished from each other, the variables are said to be
A. biased
B. blocked
C. confounded
D. stratified
E. outliers

28. 4. When the effects of two variables on a response variable cannot be distinguished from each other, the variables are said to be
A. biased
B. blocked
C. confounded
D. stratified
E. outliers

29. 5. To test a new skin rash drug, researchers decide to administer both the new drug and the standard drug, in random order, to each patient in the experimental study. That is, the researchers carrying out the study plan to use a randomized paired comparison design with repeated measures. What is the main weakness of this design?

30. 5. To test a new skin rash drug, researchers decide to administer both the new drug and the standard drug, in random order, to each patient in the experimental study. That is, the researchers carrying out the study plan to use a randomized paired comparison design with repeated measures. What is the main weakness of this design?
A. It did not use blocking.
B. The resulting data would show evidence of too much within-treatment variability.
C. The resulting data would show evidence of too much between-treatment variability.
D. There was no control group.
E. The effect of the first drug may not have worn off before the second drug was administered.

31. 5. To test a new skin rash drug, researchers decide to administer both the new drug and the standard drug, in random order, to each patient in the experimental study. That is, the researchers carrying out the study plan to use a randomized paired comparison design with repeated measures. What is the main weakness of this design?
A. It did not use blocking.
B. The resulting data would show evidence of too much within-treatment variability.
C. The resulting data would show evidence of too much between-treatment variability.
D. There was no control group.
E. The effect of the first drug may not have worn off before the second drug was administered.

32. 6. Suppose you want to study the effect of calculator use on the mathematics course grade for sixth-grade students in a district’s single middle school. In the upcoming school year, the middle school will have a total of 500 sixth-grade students.

33. 6. Suppose you want to study the effect of calculator use on the mathematics course grade for sixth-grade students in your district’s single middle school. In the upcoming school year, the middle school will have a total of 500 sixth-grade students.
Now, suppose that you plan to ask each student whether he or she uses a calculator and then compare the mean mathematics course grade for each group. Is this an observational study or an experiment? Explain.

34. Suppose that you plan to ask each student whether he or she uses a calculator and then compare the mean mathematics course grade for each group. Is this an observational study or an experiment? Explain.
It’s an observational study because the two treatments (using/not using a calculator) are not randomly assigned to the students.

35. 7. Identify which type of sampling design is being used in each scenario.
a. A school administrator randomly selects 12 classes from your school and then randomly selects 5 students from each class to study a school library issue.

36. 7. Identify which type of sampling design is being used in each scenario.
a. A school administrator randomly selects 12 classes from your school and then randomly selects 5 students from each class to study a school library issue.
two-stage cluster sample

37. 7. Identify which type of sampling design is being used in each scenario.
b. A school administrator uses random numbers to select a sample of 60 students from the roster of students enrolled in your school.

38. 7. Identify which type of sampling design is being used in each scenario.
b. A school administrator uses random numbers to select a sample of 60 students from the roster of students enrolled in your school.
simple random sample

39. c. A school administrator gets a sample of 60 students from your school by randomly selecting 15 freshmen, 15 sophomores, 15 juniors, and 15 seniors.

40. c. A school administrator gets a sample of 60 students from your school by randomly selecting 15 freshmen, 15 sophomores, 15 juniors, and 15 seniors.
stratified random sample

41. d. A school administrator uses the roster of students enrolled in your school to select a sample of students by choosing a person randomly from among the first 20 and then taking every 20th name on the roster thereafter.

42. A school administrator uses the roster of students enrolled in your school to select a sample of students by choosing a person randomly from among the first 20 and then taking every 20th name on the roster thereafter.
systematic sample with random start

43. 8. Blocking will be effective if
A. all units in one block receive the same treatment
B. each subject receives all treatments
C. units are grouped so that each block contains units that are different
D. units are grouped so that each block contains units that are similar
E. units are grouped so that each block is representative of the population

44. 8. Blocking will be effective if
A. all units in one block receive the same treatment
B. each subject receives all treatments
C. units are grouped so that each block contains units that are different
D. units are grouped so that each block contains units that are similar
E. units are grouped so that each block is representative of the population

45. 9. What is the main purpose of random selection in a sample survey?

46. 9. What is the main purpose of random selection in a sample survey?
To reduce bias and get a representative sample from the population

47. 10. Compared to simple random sampling, stratified sampling can help accomplish several goals. Which of these goals does it not advance?
A. reduce the variability associated with a statistic such as the sample mean
B. improve the precision of the results
C. provide good information on each stratum
D. make it unnecessary to use randomization
E. make it easier to take a sample

48. 10. Compared to simple random sampling, stratified sampling can help accomplish several goals. Which of these goals does it not advance?
A. reduce the variability associated with a statistic such as the sample mean
B. improve the precision of the results
C. provide good information on each stratum
D. make it unnecessary to use randomization
E. make it easier to take a sample

49. 11. There are two types of bias in sampling problems: bias due to the improper selection of sampling units and bias due to incorrect response or nonresponse. Which of these is least likely to help protect against bias?
A. random selection of sampling units
B. cluster sampling as compared to simple random sampling
C. following up with those who do not respond to the initial survey
D. designing clear and unambiguous questions
E. constructing a good sampling frame

50. 11. There are two types of bias in sampling problems: bias due to the improper selection of sampling units and bias due to incorrect response or nonresponse. Which of these is least likely to help protect against bias?
A. random selection of sampling units
B. cluster sampling as compared to simple random sampling
C. following up with those who do not respond to the initial survey
D. designing clear and unambiguous questions
E. constructing a good sampling frame

51. 12. In a northern state, these two variables are strongly associated
12. In a northern state, these two variables are strongly associated. Each case is a week during the previous year. What possible lurking variable could be responsible for this association?
I. the number of snow shovels sold at a local hardware store during the week
II. the number of school closures during that same week

52. 12.
I. the number of snow shovels sold at a local hardware store during the week
II. the number of school closures during that same week
The number of inches of snow. As the number of inches of snow increases, more and more schools close down and more equipment for shoveling snow is sold at hardware stores.

53. 13. Which of these is not a purpose or a characteristic of an experiment?
A. to compare two or more treatments
B. to estimate the parameters of a fixed, well- defined population
C. to establish cause and effect by comparing the effect of treatments on the response
D. random assignment of treatments to subjects
E. replication of each treatment on at least two subjects

54. 13. Which of these is not a purpose or a characteristic of an experiment?
A. to compare two or more treatments
B. to estimate the parameters of a fixed, well- defined population
C. to establish cause and effect by comparing the effect of treatments on the response
D. random assignment of treatments to subjects
E. replication of each treatment on at least two subjects

55. 14. Which of these will help protect against bias?
A. using a sampling process for its convenience
B. allowing volunteers to be in the sample
C. using randomization in choosing the units for the sample
D. using expert judgment in choosing the units for the sample
E. performing an observational study

56. 14. Which of these will help protect against bias?
A. using a sampling process for its convenience
B. allowing volunteers to be in the sample
C. using randomization in choosing the units for the sample
D. using expert judgment in choosing the units for the sample
E. performing an observational study

57. 15. Which of these is the definition of a biased sampling method?
A. a method that results in estimates that are too high (or too low) on the average
B. a method that usually results in estimates that are too high (or too low)
C. a method that allows people to decide for themselves whether to be in the sample
D. a method that results in a simple random sample
E. a method that results in nonrepresentative samples some of the time, but accurate estimates on the average

58. 15. Which of these is the definition of a biased sampling method?
A. a method that results in estimates that are too high (or too low) on the average
B. a method that usually results in estimates that are too high (or too low)
C. a method that allows people to decide for themselves whether to be in the sample
D. a method that results in a simple random sample
E. a method that results in nonrepresentative samples some of the time, but accurate estimates on the average

59. 16. In an experiment, if two variables are confounded, which of these statements is true?
A. One of the variables must be a lurking variable.
B. The variables will have a correlation coefficient greater than ±0.5.
C. There is a clear indication that a placebo effect is present in the experiment.
D. The investigator cannot separate the effect of the variables on a response variable.
E. None of these is true.

60. 16. In an experiment, if two variables are confounded, which of these statements is true?
A. One of the variables must be a lurking variable.
B. The variables will have a correlation coefficient greater than ±0.5.
C. There is a clear indication that a placebo effect is present in the experiment.
D. The investigator cannot separate the effect of the variables on a response variable.
E. None of these is true.

61. 17. In order to assess the membership’s attitudes about a new Supreme Court decision, a local bar association selects a simple random sample of 100 lawyers from its membership list. Surveys are delivered to the selected lawyers. Only 63 of the lawyers return their surveys. Which of these is of great concern in this situation?

62. 17. In order to assess the membership’s attitudes about a new Supreme Court decision, a local bar association selects a simple random sample of 100 lawyers from its membership list. Surveys are delivered to the selected lawyers. Only 63 of the lawyers return their surveys. Which of these is of great concern in this situation?
A. Nothing is known about the parameters of population interest.
B. Nothing is stated regarding the methodology of the simple random sample.
C. There may be a problem with the sampling frame.
D. There may be a problem with nonresponse bias.
E. None of these statements is of concern.

63. 17. In order to assess the membership’s attitudes about a new Supreme Court decision, a local bar association selects a simple random sample of 100 lawyers from its membership list. Surveys are delivered to the selected lawyers. Only 63 of the lawyers return their surveys. Which of these is of great concern in this situation?
A. Nothing is known about the parameters of population interest.
B. Nothing is stated regarding the methodology of the simple random sample.
C. There may be a problem with the sampling frame.
D. There may be a problem with nonresponse bias.
E. None of these statements is of concern.

64. Questions?