Managerial Statistics International Edition 9th Edition by Gerald Keller - Test Bank

Managerial Statistics International Edition 9th Edition by Gerald Keller – Test Bank

 

Instant Download – Complete Test Bank With Answers

 

 

Sample Questions Are Posted Below

 

CHAPTER 5 SECTION 1: DATA COLLECTION AND SAMPLING

 

TRUE/FALSE

 

1. An observational study involves collecting data about persons or objects by recording information about their selected characteristics of interest.

 

ANS:  T                    PTS:   1                    REF:   SECTION 5.1

NAT:  Analytic; Sampling

 

2. Self-administered surveys usually have a high response rate.

 

ANS:  F                    PTS:   1                    REF:   SECTION 5.1

NAT:  Analytic; Sampling

 

3. In designing a survey, demographic questions must be avoided.

 

ANS:  F                    PTS:   1                    REF:   SECTION 5.1

NAT:  Analytic; Sampling

 

4. The response rate of a survey is the proportion of all people who were selected but did not complete the survey.

 

ANS:  F                    PTS:   1                    REF:   SECTION 5.1

NAT:  Analytic; Sampling

 

5. A self-selected sample is the group of individuals who were randomly selected to be in the sample, then agreed to participate in the study.

 

ANS:  F                    PTS:   1                    REF:   SECTION 5.1

NAT:  Analytic; Sampling

 

6. Experimental data tend to be more reliable, or “stronger,” than survey data.

 

ANS:  T                    PTS:   1                    REF:   SECTION 5.1

NAT:  Analytic; Sampling

 

7. An experiment involves collecting data about persons or objects by deliberately exposing them to some kind of change and comparing the results.

 

ANS:  T                    PTS:   1                    REF:   SECTION 5.1

NAT:  Analytic; Sampling

 

8. A question on a survey that was not answered is an example of an open-ended question.

 

ANS:  F                    PTS:   1                    REF:   SECTION 5.1

NAT:  Analytic; Sampling

 

 

9. A self-selected sample is one in which the individuals choose themselves to be in the sample.

 

ANS:  T                    PTS:   1                    REF:   SECTION 5.1

NAT:  Analytic; Sampling

 

10. “Wouldn’t you agree that foreign cars are better than American cars?” is an example of a well-worded survey question.

 

ANS:  F                    PTS:   1                    REF:   SECTION 5.1

NAT:  Analytic; Sampling

 

MULTIPLE CHOICE

 

11. Which method of data collection is involved when a researcher counts and records the number of students wearing backpacks on campus in a given day?

a.	An experiment.
b.	A survey.
c.	Direct observation.
d.	None of these choices.

 

 

ANS:  C                    PTS:   1                    REF:   SECTION 5.1

NAT:  Analytic; Sampling

 

12. Which of the following statements is true regarding the design of a good survey?

a.	The questions should be kept as short as possible.
b.	A mixture of dichotomous, multiple-choice, and open-ended questions may be used.
c.	Leading questions must be avoided.
d.	All of these choices are true.

 

 

ANS:  D                    PTS:   1                    REF:   SECTION 5.1

NAT:  Analytic; Sampling

 

13. A marketing research firm selects a random sample of adults and asks them a list of questions regarding their beverage preferences. What type of data collection is involved here?

a.	An experiment.
b.	A survey.
c.	Direct observation.
d.	None of these choices.

 

 

ANS:  B                    PTS:   1                    REF:   SECTION 5.1

NAT:  Analytic; Sampling

 

14. Which of the following must be avoided in designing a survey?

a.	Dichotomous questions.
b.	Leading questions.
c.	Demographic questions.
d.	All of these choices are true.

 

 

ANS:  B                    PTS:   1                    REF:   SECTION 5.1

NAT:  Analytic; Sampling

 

15. A researcher conducts a study where she divides subjects into two groups, gives each group a certain treatment, and records their responses. What type of data collection is being used here?

a.	An experiment.
b.	Direct observation.
c.	A survey.
d.	A census.

 

 

ANS:  A                    PTS:   1                    REF:   SECTION 5.1

NAT:  Analytic; Sampling

 

16. The personnel director at a large company studied the eating habits of the company’s employees. The director watched and recorded whether each employee brought his/her own lunch to work, ate at the company cafeteria, or went out to lunch. What method of data collection was used here?

a.	Direct observation.
b.	An experiment.
c.	A survey.
d.	A personal interview.

 

 

ANS:  A                    PTS:   1                    REF:   SECTION 5.1

NAT:  Analytic; Sampling

 

17. Which of the following data collection methods is not observational?

a.	A personal interview.
b.	A telephone interview.
c.	A self-administered questionnaire.
d.	An experiment.

 

 

ANS:  D                    PTS:   1                    REF:   SECTION 5.1

NAT:  Analytic; Sampling

 

COMPLETION

 

18. In a(n) ____________________ study, there is no attempt to control factors that might influence the variable of interest.

 

ANS:  observational

 

PTS:   1                    REF:   SECTION 5.1                                 NAT:  Analytic; Sampling

 

19. The ____________________ rate is the proportion of people in the sample who completed the survey.

 

ANS:  response

 

PTS:   1                    REF:   SECTION 5.1                                 NAT:  Analytic; Sampling

 

20. In a(n) ____________________ study, individuals are randomly assigned to different treatments and the results are compared.

 

ANS:  experimental

 

PTS:   1                    REF:   SECTION 5.1                                 NAT:  Analytic; Sampling

 

21. A survey is an example of a(n) ____________________ study.

 

ANS:  observational

 

PTS:   1                    REF:   SECTION 5.1                                 NAT:  Analytic; Sampling

 

22. Two types of interviews that are used to collect data are ____________________ interviews and ____________________ interviews.

 

ANS:

personal; telephone

telephone; personal

 

PTS:   1                    REF:   SECTION 5.1                                 NAT:  Analytic; Sampling

 

23. In a self-administered survey, the individuals in the sample are typically contacted by ____________________.

 

ANS:  mail

 

PTS:   1                    REF:   SECTION 5.1                                 NAT:  Analytic; Sampling

 

24. Gender, occupation, and age are all examples of ____________________ variables.

 

ANS:  demographic

 

PTS:   1                    REF:   SECTION 5.1                                 NAT:  Analytic; Sampling

 

SHORT ANSWER

 

25. Describe the difference between an observational study and an experimental study.

 

ANS:

In an observational study, there is no attempt to control factors that might influence the variable of interest. In an experimental study, a factor (such as regular use of fitness center) is controlled by randomly selecting who is exposed to that factor, thereby reducing the influence of other factors on the variable of interest.

 

PTS:   1                    REF:   SECTION 5.1                                  NAT:  Analytic; Sampling

 

26. Briefly discuss three methods of conducting a survey of people.

 

ANS:

 

a.	Personal interview: involves an interviewer soliciting information from a respondent by asking prepared questions; it has a higher expected response rate but is typically expensive.

 

 

b.	Telephone interview: involves soliciting information by calling people. This is usually less expensive, but it is also less personal and has a lower expected response rate.
c.	Self-administered survey: this is an inexpensive method of conducting a survey which is usually mailed to a sample of people; it usually has a very low response rate.

 

 

PTS:   1                    REF:   SECTION 5.1                                 NAT:  Analytic; Sampling

 

27. Give three important points to consider when designing a questionnaire.

 

ANS:

Any three of the following are acceptable:

 

a.	Keep the questionnaire as short as possible.
b.	Design the questions to be short, simple, and clearly worded.
c.	Consider beginning with simple demographic questions to help respondents get started and become comfortable quickly.
d.	Consider using a combination of dichotomous questions, multiple-choice questions, and open-ended questions.
e.	Avoid using leading questions.
f.	When preparing the questions, think about how you intend to tabulate and analyze the responses.

 

 

PTS:   1                    REF:   SECTION 5.1                                 NAT:  Analytic; Sampling

 

28. List one advantage and one disadvantage of a telephone interview as a method of data collection.

 

ANS:

Advantage: It is usually less expensive than other methods of data collection.

 

Disadvantages: It is less personal, has a lower expected response rate, and many people will refuse to respond to telephone surveys unless the issue is of interest to them.

 

PTS:   1                    REF:   SECTION 5.1                                 NAT:  Analytic; Sampling

 

29. List one advantage and one disadvantage of a personal interview as a method of data collection.

 

ANS:

Advantages: It has a higher expected response rate than other methods of data collection. In addition, there will probably be fewer incorrect responses resulting from respondents misunderstanding some questions, because the interviewer, if asked, can clarify misunderstandings.

 

Disadvantages: It has the potential for bias if the interviewer says too much whenever asked to clarify misunderstandings of some questions. The main disadvantage of personal interviews is that they are expensive, especially when travel is involved.

 

PTS:   1                    REF:   SECTION 5.1                                 NAT:  Analytic; Sampling

 

 

30. Discuss one advantage and one disadvantage of a self-administered survey as a method of data collection.

 

ANS:

Advantages: It is an inexpensive method of conducting a survey, since it is usually mailed to a sample of people, and is therefore attractive when the number of people to be surveyed is large.

 

Disadvantages: Self-administered surveys usually have low response rates and may have a relatively high number of incorrect responses due to respondents misunderstanding some questions.

 

PTS:   1                    REF:   SECTION 5.1                                 NAT:  Analytic; Sampling

 

Soft Drinks

 

A soft drink manufacturer has been supplying its products in bottles to grocery stores and in cans to small convenience stores. The company is analyzing sales of this product to determine which type of packaging is preferred by customers.

 

 

31. {Soft Drink Narrative} Is this study observational or experimental? Explain.

 

ANS:

The study is observational. The statistics practitioner did not randomly assign stores to selling bottles or cans. Type of store and type of packaging cannot be separated here.

 

PTS:   1                    REF:   SECTION 5.1                                 NAT:  Analytic; Sampling

 

32. {Soft Drink Narrative} Outline a better method for designing this study, so the same types of stores don’t get the same types of packaging.

 

ANS:

Randomly assign some grocery stores to receive bottles and the other grocery stores to receive cans. Randomly assign some convenience stores to receive bottles and the other convenience stores to receive cans. Or, have each store (convenience or grocery) carry both bottles and cans.

 

PTS:   1                    REF:   SECTION 5.1                                 NAT:  Analytic; Sampling

 

Smoking and Heart Attacks

 

A medical researcher is interested in investigating the relationship between smoking and heart attacks

 

 

 

33. {Smoking and Heart Attacks Narrative} Briefly describe how the researcher might design an observational study to investigate the relationship between smoking and heart attacks

 

ANS:

Randomly sample a group of smokers and randomly sample a group of nonsmokers. Follow these individuals and find the proportion of each group that has a heart attack. Or, sample a group of individuals that had a heart attack and find out what proportion of them smoked and what proportion did not smoke.

 

PTS:   1                    REF:   SECTION 5.1                                 NAT:  Analytic; Sampling

 

34. {Smoking and Heart Attacks Narrative} What type of studies are plausible in this particular scenario, observational studies or experiments?

 

ANS:

Observational studies are the only choice here. Experimental data would require the medical researcher to randomly assign some people to smoke and others not to smoke. This of course is not ethical.

 

PTS:   1                    REF:   SECTION 5.1                                 NAT:  Analytic; Sampling

 

35. {Smoking and Heart Attacks Narrative} How can you show that smoking causes heart attacks without being able to do a designed experiment?

 

ANS:

Instead of conducting one simple observational study, conduct many observational studies, each looking at smoking and heart attacks from a different angle, for all different populations. Once the entire body of evidence from all these studies is examined, the connection can be seen between smoking and heart attacks.

 

PTS:   1                    REF:   SECTION 5.1                                  NAT:  Analytic; Sampling

 

CHAPTER 5 SECTION 2-4: DATA COLLECTION AND SAMPLING

 

TRUE/FALSE

 

36. A person receives a mail survey and shreds it without opening it. This causes nonresponse error.

 

ANS:  T                    PTS:   1                    REF:   SECTION 5.2-5.4

NAT:  Analytic; Sampling

 

37. Self-selected samples have no bias because they are chosen by the people themselves.

 

ANS:  F                    PTS:   1                    REF:   SECTION 5.2-5.4

NAT:  Analytic; Sampling

 

38. A cluster sample occurs when you randomly select groups, and for each group selected, you sample every single member of that group.

 

ANS:  T                    PTS:   1                    REF:   SECTION 5.2-5.4

NAT:  Analytic; Sampling

 

39. The larger the sample size is, the more accurate we can expect our sample estimates to be.

 

ANS:  T                    PTS:   1                    REF:   SECTION 5.2-5.4

NAT:  Analytic; Sampling

 

40. Selection bias occurs when researchers select biased questions to include on a survey.

 

ANS:  F                    PTS:   1                    REF:   SECTION 5.2-5.4

NAT:  Analytic; Sampling

 

41. The target population is the population about which we want to draw inferences and conclusions, while the sampled population is the actual population from which the sample has been taken.

 

ANS:  T                    PTS:   1                    REF:   SECTION 5.2-5.4

NAT:  Analytic; Sampling

 

42. A target population and a sampled population mean the same thing.

 

ANS:  F                    PTS:   1                    REF:   SECTION 5.2-5.4

NAT:  Analytic; Sampling

 

43. A self-selected sample represents the sampled population but not the target population.

 

ANS:  T                    PTS:   1                    REF:   SECTION 5.2-5.4

NAT:  Analytic; Sampling

 

44. A nonsampling error can be caused by the wording of a question.

 

ANS:  T                    PTS:   1                    REF:   SECTION 5.2-5.4

NAT:  Analytic; Sampling

 

45. When responses are not obtained from some members of the sample, bias is introduced.

 

ANS:  T                    PTS:   1                    REF:   SECTION 5.2-5.4

NAT:  Analytic; Sampling

 

46. A sampling error can be reduced by taking a larger sample size.

 

ANS:  T                    PTS:   1                    REF:   SECTION 5.2-5.4

NAT:  Analytic; Sampling

 

47. Sampling error refers to the difference between the sample and the population that exists only because of the observations that happened to be selected for the sample by chance.

 

ANS:  T                    PTS:   1                    REF:   SECTION 5.2-5.4

NAT:  Analytic; Sampling

 

48. Sampling error is the result of a mistake made during the sampling process.

 

ANS:  F                    PTS:   1                    REF:   SECTION 5.2-5.4

NAT:  Analytic; Sampling

 

49. Cluster samples typically cost less but they also increase sampling error.

 

ANS:  T                    PTS:   1                    REF:   SECTION 5.2-5.4

NAT:  Analytic; Sampling

 

50. A simple random sample is chosen in such a fashion that every possible subset of the same size has an equal chance of being selected.

 

ANS:  T                    PTS:   1                    REF:   SECTION 5.2-5.4

NAT:  Analytic; Sampling

 

51. Nonresponse error occurs when responses are not obtained from some members of the sample.

 

ANS:  T                    PTS:   1                    REF:   SECTION 5.2-5.4

NAT:  Analytic; Sampling

 

52. Nonresponse error occurs when someone was not selected to participate in the survey.

 

ANS:  F                    PTS:   1                    REF:   SECTION 5.2-5.4

NAT:  Analytic; Sampling

 

53. Selection bias is a systematic tendency to favor including individuals with particular characteristics, while excluding individuals with other characteristics.

 

ANS:  T                    PTS:   1                    REF:   SECTION 5.2-5.4

NAT:  Analytic; Sampling

 

 

54. To reduce sampling error, minimize the chance for bias to occur during sampling.

 

ANS:  F                    PTS:   1                    REF:   SECTION 5.2-5.4

NAT:  Analytic; Sampling

 

MULTIPLE CHOICE

 

55. When every possible sample with the same number of observations is equally likely to be chosen, the result is called a:

a.	simple random sample.
b.	stratified random sample.
c.	cluster sample.
d.	biased sample.

 

 

ANS:  A                    PTS:   1                    REF:   SECTION 5.2-5.4

NAT:  Analytic; Sampling

 

56. The manager of the customer service division of a major consumer electronics company is interested in determining whether the customers who have purchased a videocassette recorder over the past 12 months are satisfied with their products. If there are 4 different brands of videocassette recorders made by the company, the best sampling strategy would be to use a:

a.	simple random sample.
b.	stratified random sample.
c.	cluster sample.
d.	self-selected sample.

 

 

ANS:  B                    PTS:   1                    REF:   SECTION 5.2-5.4

NAT:  Analytic; Sampling

 

57. Which of the following causes sampling error?

a.	Taking a random sample from a population instead of studying the entire population.
b.	Making a mistake in the process of collecting the data.
c.	Nonresponse bias.
d.	All of these choices are true.

 

 

ANS:  A                    PTS:   1                    REF:   SECTION 5.2-5.4

NAT:  Analytic; Sampling

 

58. A pharmaceutical company interested in measuring how often physicians prescribe a certain drug has selected a simple random sample from each of two groups: M.D. (Medical Doctors) and D.O. (Osteopaths). What is this type of sampling called?

a.	Simple random sampling.
b.	Cluster sampling.
c.	Stratified random sampling.
d.	None of these choices.

 

 

ANS:  C                    PTS:   1                    REF:   SECTION 5.2-5.4

NAT:  Analytic; Sampling

 

 

59. When the population is divided into mutually exclusive sets, and then a simple random sample is drawn from each set, this is called:

a.	simple random sampling.
b.	stratified random sampling.
c.	cluster sampling.
d.	selection bias.

 

 

ANS:  B                    PTS:   1                    REF:   SECTION 5.2-5.4

NAT:  Analytic; Sampling

 

60. Which of the following types of samples is almost always biased?

a.	Simple random samples.
b.	Stratified random samples.
c.	Cluster samples.
d.	Self-selected samples.

 

 

ANS:  D                    PTS:   1                    REF:   SECTION 5.2-5.4

NAT:  Analytic; Sampling

 

61. The difference between a sample mean and the population mean is called:

a.	nonresponse error.
b.	selection bias.
c.	sampling error.
d.	nonsampling error.

 

 

ANS:  C                    PTS:   1                    REF:   SECTION 5.2-5.4

NAT:  Analytic; Sampling

 

62. Which of the following types of samples should not be used to make good statistical inferences from a sample to a population?

a.	Stratified random samples.
b.	Self-selected samples.
c.	Cluster samples.
d.	All of these choices are true.

 

 

ANS:  D                    PTS:   1                    REF:   SECTION 5.2-5.4

NAT:  Analytic; Sampling

 

63. Which of the following is an example of a nonsampling error?

a.	Some incorrect responses are recorded.
b.	Responses are not obtained from all members of the sample.
c.	Some members of the target population cannot possibly be selected for the sample.
d.	All of these choices are true.

 

 

ANS:  D                    PTS:   1                    REF:   SECTION 5.2-5.4

NAT:  Analytic; Sampling

 

64. The Admissions Officer from a large university mailed a survey to 600 students selected at random. The sample was designed to include 150 students randomly selected from each of the freshman, sophomore, junior, and senior classes on campus. What sampling method was used?

a.	Simple random sample
b.	Systematic sample
c.	Stratified random sample
d.	Cluster sample

 

 

ANS:  C                    PTS:   1                    REF:   SECTION 5.2-5.4

NAT:  Analytic; Sampling

 

65. Which of the following situations lends itself to cluster samples?

a.	When it is difficult to develop a complete list of the population members.
b.	When the population members are widely dispersed.
c.	When selecting and collecting data from a simple random sample is too costly.
d.	All of these choices are true.

 

 

ANS:  D                    PTS:   1                    REF:   SECTION 5.2-5.4

NAT:  Analytic; Sampling

 

66. To give away a door prize, the hostess of a Tupperware party put each person’s name into a hat, mixed them up, and selected one name. What sampling method was used?

a.	Simple random sample
b.	Systematic sample
c.	Stratified random sample
d.	Cluster sample

 

 

ANS:  A                    PTS:   1                    REF:   SECTION 5.2-5.4

NAT:  Analytic; Sampling

 

67. Which of the following describes selection bias?

a.	A leading question is selected for inclusion in the survey.
b.	Some members of the target population are excluded from possible selection for the sample.
c.	A person selected for the sample has a biased opinion about the survey.
d.	All of these choices are true.

 

 

ANS:  B                    PTS:   1                    REF:   SECTION 5.2-5.4

NAT:  Analytic; Sampling

 

COMPLETION

 

68. Proper interviewer training helps to reduce ____________________ error.

 

ANS:  nonsampling

 

PTS:   1                    REF:   SECTION 5.2-5.4                           NAT:  Analytic; Sampling

 

69. Excluding some members of the target population results in ____________________ bias.

 

ANS:  selection

 

PTS:   1                    REF:   SECTION 5.2-5.4                           NAT:  Analytic; Sampling

 

 

70. ____________________ error results from the failure to collect data from all subjects in the sample.

 

ANS:  Nonresponse

 

PTS:   1                    REF:   SECTION 5.2-5.4                           NAT:  Analytic; Sampling

 

71. ____________________ error refers to differences between the sample and the population.

 

ANS:  Sampling

 

PTS:   1                    REF:   SECTION 5.2-5.4                           NAT:  Analytic; Sampling

 

72. ____________________ error is due to mistakes made in the acquisition of data.

 

ANS:  Nonsampling

 

PTS:   1                    REF:   SECTION 5.2-5.4                           NAT:  Analytic; Sampling

 

73. A(n) ____________________ sample is obtained by separating the population into groups and taking a simple random sample from each group.

 

ANS:

stratified

stratified random

 

PTS:   1                    REF:   SECTION 5.2-5.4                           NAT:  Analytic; Sampling

 

74. ____________________ sampling is particularly useful when it is difficult or costly to develop a complete list of the population members.

 

ANS:  Cluster

 

PTS:   1                    REF:   SECTION 5.2-5.4                           NAT:  Analytic; Sampling

 

SHORT ANSWER

 

75. What is meant by a self-selected sample? Why are self-selected samples not desirable?

 

ANS:

A self-selected sample is a sample formed primarily on the basis of voluntary inclusion, with little control by the designer of the survey. Self-selected samples are usually biased, because those who participate are more interested in the issue than those who don’t, and therefore probably have a different opinion.

 

PTS:   1                    REF:   SECTION 5.2-5.4                           NAT:  Analytic; Sampling

 

 

76. A senator wants to estimate the mean age of registered voters in her state. Unfortunately, she does not have a complete list of households in her state. Describe a sampling plan that would be suitable for her purposes.

 

ANS:

Use cluster sampling, where each city block is a cluster. Select a certain number of state counties at random, then for each city block selected, sample each household in that county.

 

PTS:   1                    REF:   SECTION 5.2-5.4                           NAT:  Analytic; Sampling

 

77. The Chairman of a College of Business with five departments wants to estimate the average number of student-hours lost per month due to illness of their professors. Describe a sampling plan that will help the Dean compare the average student-loss hours for the five departments.

 

ANS:

The Chairman can take one simple random sample from each department for comparison purposes. That means he is taking a stratified random sample, where the strata are the five departments.

 

PTS:   1                    REF:   SECTION 5.2-5.4                           NAT:  Analytic; Sampling

 

78. Briefly describe three types of nonsampling errors.

 

ANS:

 

a.	Errors in data acquisition: Errors that arise from the recording of incorrect responses.
b.	Nonresponse error: Errors that arise when responses are not obtained from some members of the sample.
c.	Selection bias: Errors that arise when some members of the target population cannot possibly be selected for the sample.

 

 

PTS:   1                    REF:   SECTION 5.2-5.4                           NAT:  Analytic; Sampling

 

79. Pollsters want to know what percentage of all registered voters in Missoula, Montana, intend to vote in the next election. They visit with 350 people at the downtown shopping mall during one afternoon and ask each person whether or not they intend to vote. Are the target population and the sampled population the same in this case? Explain.

 

ANS:

In this situation, the target population and the sampled population are not the same. The target population consists of all registered voters in Missoula, Montana. The sampled population, however, consists of anyone in Missoula who was at that mall that afternoon (registered voters or not), thereby excluding a very large portion of the Missoula, Montana, registered voters.

 

PTS:   1                    REF:   SECTION 5.2-5.4                           NAT:  Analytic; Sampling

 

 

80. Give an example of a poll that involves a self-selected sample.

 

ANS:

Choose any recent radio or television poll based on responses of listeners who phone in on a volunteer basis. Another example is a survey that appears on an Internet website.

 

PTS:   1                    REF:   SECTION 5.2-5.4                           NAT:  Analytic; Sampling

 

81. Is it possible for a sample to yield better results than a census, from a practical standpoint? Explain.

 

ANS:

Yes. In any case where the population is large in size, a census will likely contain significantly more nonsampling errors than a carefully conducted sample survey.

 

PTS:   1                    REF:   SECTION 5.2-5.4                           NAT:  Analytic; Sampling

 

82. A regular feature in many newspapers asks readers to respond via e-mail to a survey question. The percentages of yes and no responses are usually reported the following day. Should we ignore the results of these surveys? Explain.

 

ANS:

Yes, we should ignore the results because this is an example of a self-selected sample. Self-selected samples are almost always biased because they tend to only represent those with strong opinions.

 

PTS:   1                    REF:   SECTION 5.2-5.4                           NAT:  Analytic; Sampling