1.1Target population: Unclear, but presumed to be readers ofTimemagazine.

Chapter 1 Introduction

1.1Target population: Unclear, but presumed to be readers ofTimemagazine.

Sampling frame: Persons who know about the online survey.

Sampling unit=observation unit: One response to the survey.

As noted in Section 1.3, samples that consist only of volunteers are suspect. This is especially true of surveys in which respondents must register and provide personal information to participate, as here. This survey is likely not intended to provide input to the editors, but rather to provide readers a way of feeling connected and involved with the magazine.It also is possible that persons with strong opinions about the band BTS organized and contributed multiple responses to the poll.

1.2Target population: All mutual funds.

Sampling frame: Mutual funds in the list.

Sampling unit=observation unit: One listing.

As funds are listed alphabetically by company, there is no reason to believe there will be any selection bias from the sampling frame. There may be undercoverage, however, if smaller or new funds are not listed in the newspaper.

1.3Target population: Not specied, but a target population of interest would be persons who have read the book.

Sampling frame: Persons who visit the website

Sampling unit=observation unit: One review.

The reviews are contributed by volunteers. They cannot be taken as representative of readers' 1 Solutions Manual for Sampling Design and Analysis, 3e by Sharon Lohr (All Chapters) 1 / 4

2CHAPTER 1. INTRODUCTION

opinions. Indeed, there have been instances where authors of competing books have written negative reviews of a book, or a book's author manages to ood the site with positive reviews.

1.4Target population: Persons eligible for jury duty in Pennsylvania.

Sampling frame: State residents who are registered voters or licensed drivers over 18.

Sampling unit=observation unit: One resident.

Selection bias occurs largely because of undercoverage and nonresponse. Eligible jurors may not appear in the sampling frame because they are not registered to vote and they do not possess an Arizona driver's license. Addresses on either list may not be up to date. In addition, jurors fail to appear or are excused; this is nonresponse.

1.5Target population: All persons experiencing homelessness in study area.

Sampling frame: Clinics participating in the Health Care for the Homeless project.Sampling unit: Unclear. Depending on assumptions made about the survey design, one could say either a clinic or a person is the sampling unit.

Observation unit: Person.

Selection bias may be a serious problem for this survey. Even though the demographics for HCH patients are claimed to match those of the homeless population (but do weknowthey match?) and the clinics are readily accessible, the patients dier in two critical ways from non-patients: (1) they needed medical treatment, and (2) they went to a clinic to get medical treatment. One does not know the likely direction of selection bias, but there is no reason to believe that the same percentages of patients and non-patients are mentally ill.

1.6Target population: Likely voters in Iowa.

Sampling frame: Persons who attend the State Fair and stop by the booth.

Sampling unit=observation unit: One person.

This is a convenience sample of volunteers, and we cannot trust any statistics from it.

1.7Target population: All cows in region.

Sampling frame: List of all farms in region.

Sampling unit: One farm.

Observation unit: One cow.

There is no reason to anticipate selection bias in this survey. The design is a single-stage cluster sample, discussed in Chapter 5.

1.8Target population: Licensed boarding homes for the elderly in Washington state.

Sampling frame: List of 184 licensed homes.

Sampling unit=observation unit: One home. 2 / 4

3 Nonresponse is the obvious problem here, with only 43 of 184 administrators or food service man- agers responding. It may be that the respondents are the larger homes, or that their menus have better nutrition. The problem with nonresponse, though, is that we can only conjecture the direc- tion of the nonresponse bias.

1.9Target population: Wikipedia science articles.

Sampling frame: Articles thought to be of interest by the sampler.

Sampling unit: One article.

This is a judgment sample, where the articles are deliberately chosen for review. The statistics apply only to the sample, and cannot be generalized to the population. There is additional possible selection bias because of the nonresponse; perhaps articles with many or few errors are harder to get reviewers for.

1.10Target population: The 32,000 subscribers to the magazine.

Sampling frame: Magazine subscribers who saw the survey invitation.

Sampling unit: One response. Since more than 32,000 responses were received, it appears that either non-subscribers responded to the survey or some subscribers responded multiple times.This is a convenience sample. The statistics have no validity because of the self-selected nature of the sample. A person who responded multiple times could unduly inuence the survey results. In many surveys of this type, only persons with strong opinions respond. It's possible in this case that persons who have been inconvenienced by a PC malfunction will be more likely to respond than persons who have experienced no problems with their PCs.

1.11Target population: Unclear. Presumably they want to generalize the results to adult women.

Sampling frame: Persons who see and respond to the online invitation.

Sampling unit: One response. It is possible that some persons responded multiple times.This is a convenience sample. The statistics have no validity because of the self-selected nature of the sample. We don't even know if 4,000 dierent women responded, or even if the respondents are women; it could be just a handful of persons each responding multiple times.

1.12Target population: Faculty members at higher education institutions.

Sampling frame: Faculty members in the purposively sampled institutions. The authors did not state how they selected the faculty in those institutions who were surveyed.

Sampling unit: One faculty member.

There are several sources of selection bias. The rst is the purposive nature of the college sample.Although the authors stated that the institutions are representative in terms of institutional type, geographic and demographic diversity, religious/nonreligious aliation, and the public/private di- mension, it is very easy for conscious or unconscious subjective biases to skew such a sample.A second source of potential bias comes from the selection of faculty to participate (if not every- 3 / 4

4CHAPTER 1. INTRODUCTION

one or a random sample). Finally, only about 60% of the selected faculty members respond, so nonresponse is another potential source of bias.

1.13Target population: All ASA members.

Sampling frame: ASA members with active e-mail addresses.

Sampling unit: One member.

ASA members could respond only if e-mailed the survey, and this ensured that each member responded at most once. But the low response rate raises concerns that the respondents may be persons who are strongly engaged in the topic.

1.14Target population: All married couples in the U.S.

Sampled population: Married couples who were in therapy or counseling

Sampling unit: One counselor

Observation unit: One couple

Couples in therapy may be experiencing more marital problems than other couples.

1.15Target population: All adults

Sampling frame: Friends and relatives of American Cancer Society volunteers

Sampling unit: One person

This is a convenience sample, and the results cannot be applied to the general population. Here's

what I wrote about the survey elsewhere:

Although the sample contained Americans of diverse ages and backgrounds, and the sample may have provided valuable information for exploring factors associated with development of cancer, its validity for investigating the relationship between amount of sleep and mortality is questionable.The questions about amount of sleep and insomnia were not the focus of the original study, and the survey was not designed to obtain accurate responses to those questions. The design did not allow researchers to assess whether the sample was representative of the target population of all Americans. Because of the shortcomings in the survey design, it is impossible to know whether the conclusions in Kripke et al. (2002) about sleep and mortality are valid or not. (Lohr, 2008, pp. 9798)

1.16Target population: Readers of romance ction

Sampled population: Women who self-identied as readers of romance ction

Sampling unit: One woman

Observation unit: One woman

This was almost certainly a convenience sample.

1.17Target population: All statisticians

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