, Solutions Manual for
Sampling: Design and Analysis
Second Edition
by
Sharon L. Lohr
CHAPTER 1
INTRODUCTION
1.1 Target population: Unclear, but presumed to be readers of Parade magazine.
Sampling frame: Persons who know about the telephone survey.
Sampling unit = observation unit: One call. (Although it would also be correct to
consider the sampling unit to be a person. The survey is so badly done that it is
difficult to tell what the units are.)
As noted in Section 1.3, samples that consist only of volunteers are suspect. This
is especially true of surveys in which respondents must pay to participate, as
here— persons willing to pay 75 cents a call are likely to have strong opinions
about the legalization of marijuana, and it is impossible to say whether pro- or
,anti-legalization adherents are more likely to call. This survey is utterly worthless
for measuring public opinion because of its call-in format. Other potential biases,
such as requiring a touch-tone telephone, or the sensitive subject matter or the
ambiguity of the wording (what does “as legal as alcoholic beverages” mean?)
probably make little difference because the call-in structure destroys all
credibility for the survey by itself.
1.2 Target population: All mutual funds.
Sampling frame: Mutual funds listed in newspaper.
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.
1.3 Target population: Not specified, 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.
1
CHAPTER 1. INTRODUCTION
The reviews are contributed by volunteers. They cannot be taken as
representative of readers’ opinions. Indeed, there have been instances where
authors of competing books have written negative reviews of a book, although
amazon.com tries to curb such practices.
1.4 Target population: Persons eligible for jury duty in Maricopa County.
Sampling frame: County 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.
A similar question for class discussion is whether there was selection bias in
selecting which young men in the U.Sw˙ ere to be drafted and sent to Vietnam.
1.5 Target population: All homeless persons in study area.
Sampling frame: Clinics participating in the Health Care for the Homeless project.
, 2
Sampling unit: Unclear. Depending on assumptions made about the survey design,
one could say either a clinic or a homeless 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 we know they match?) and the clinics are readily accessible,
the patients differ 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.
1.6 Target population: Female readers of Prevention magazine.
Sampling frame: Women who see the survey in a copy of the magazine.
Sampling unit = observation unit: One woman.
This is a mail-in survey of volunteers, and we cannot trust any statistics from it.
1.7 Target 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-
3
stage cluster sample, discussed in CHAPTER 5.
1.8 Target population: Licensed boarding homes for the elderly in Washington
state.
Sampling frame: List of 184 licensed homes.
Sampling unit = observation unit: One home.
Nonresponse is the obvious problem here, with only 43 of 184 administrators or
food service managers 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 direction of the nonresponse bias.
1.13 Target population: All attendees of the 2005 JSM.
Sampling population: E-mail addresses provided by the attendees of the 2005
JSM.
Sampling unit: One e-mail address.
Sampling: Design and Analysis
Second Edition
by
Sharon L. Lohr
CHAPTER 1
INTRODUCTION
1.1 Target population: Unclear, but presumed to be readers of Parade magazine.
Sampling frame: Persons who know about the telephone survey.
Sampling unit = observation unit: One call. (Although it would also be correct to
consider the sampling unit to be a person. The survey is so badly done that it is
difficult to tell what the units are.)
As noted in Section 1.3, samples that consist only of volunteers are suspect. This
is especially true of surveys in which respondents must pay to participate, as
here— persons willing to pay 75 cents a call are likely to have strong opinions
about the legalization of marijuana, and it is impossible to say whether pro- or
,anti-legalization adherents are more likely to call. This survey is utterly worthless
for measuring public opinion because of its call-in format. Other potential biases,
such as requiring a touch-tone telephone, or the sensitive subject matter or the
ambiguity of the wording (what does “as legal as alcoholic beverages” mean?)
probably make little difference because the call-in structure destroys all
credibility for the survey by itself.
1.2 Target population: All mutual funds.
Sampling frame: Mutual funds listed in newspaper.
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.
1.3 Target population: Not specified, 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.
1
CHAPTER 1. INTRODUCTION
The reviews are contributed by volunteers. They cannot be taken as
representative of readers’ opinions. Indeed, there have been instances where
authors of competing books have written negative reviews of a book, although
amazon.com tries to curb such practices.
1.4 Target population: Persons eligible for jury duty in Maricopa County.
Sampling frame: County 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.
A similar question for class discussion is whether there was selection bias in
selecting which young men in the U.Sw˙ ere to be drafted and sent to Vietnam.
1.5 Target population: All homeless persons in study area.
Sampling frame: Clinics participating in the Health Care for the Homeless project.
, 2
Sampling unit: Unclear. Depending on assumptions made about the survey design,
one could say either a clinic or a homeless 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 we know they match?) and the clinics are readily accessible,
the patients differ 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.
1.6 Target population: Female readers of Prevention magazine.
Sampling frame: Women who see the survey in a copy of the magazine.
Sampling unit = observation unit: One woman.
This is a mail-in survey of volunteers, and we cannot trust any statistics from it.
1.7 Target 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-
3
stage cluster sample, discussed in CHAPTER 5.
1.8 Target population: Licensed boarding homes for the elderly in Washington
state.
Sampling frame: List of 184 licensed homes.
Sampling unit = observation unit: One home.
Nonresponse is the obvious problem here, with only 43 of 184 administrators or
food service managers 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 direction of the nonresponse bias.
1.13 Target population: All attendees of the 2005 JSM.
Sampling population: E-mail addresses provided by the attendees of the 2005
JSM.
Sampling unit: One e-mail address.
