Transcript Sample

Outline: Survey Research
 I. Sampling
 II. Survey Contents
I. Sampling from a Population
“Sampling is the process of selecting units (e.g., people,
organizations) from a population of interest so that by
studying the sample we may fairly generalize our
results back to the population from which they were
chosen.”
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Population - complete set of individuals having some
common characteristic
– e.g., Australians
Sampling frame – subset of the population from which
the sample is actually drawn
– e.g., White pages
Sample – the set of people included in the study (i.e.,
selected from the sampling frame)
– e.g., Every 1000th person in the white pages
Population and Sample
Population
Sample
Use statistics to
summarize features
Use parameters to
summarize features
Inference on the population from the sample
Confidence Intervals
 The problem is to use the sample to make inferences
about the population
 If we were to repeat the entire process of drawing a
sample and computing the statistic many, many
times, we would find that the statistic varies some
 A confidence interval takes advantage of those
variations and allows us to specify a range that
probably contains the true value of the parameter
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Technically, for an X% confidence interval, the
parameter will fall inside the specified range X% of the
time in repetitions of the study
Confidence intervals usually vary between 90% and
99.9%
Define a Population
 The first step in choosing a sample is to
define the population, or the overall set of
cases that we’re interested in
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If we want to predict the results of an election,
then our population is “likely voters”
If we want to understand who decides to vote,
then our population is “citizens eligible to vote”
If we want to understand who decides to use
marijuana in the United States, our population
is probably “everyone in the United States”
Types of Samples Used
 Nonprobability Sample
 Items included are chosen without
regard to their probability of occurrence
 Probability Sample
 Items in the sample are chosen on the
basis of known probabilities
Types of Sampling Methods
Samples
Non-Probability
Samples
Probability Samples
Simple
Random
Convenience
Quota
Stratified
Cluster
Probability Sampling
 Members of the sample are chosen based on
known probabilities
Probability Samples
Simple
Random
Stratified
Cluster
Simple Random Samples
 Every individual or item from the frame has an
equal chance of being selected
 Selection may be with replacement or without
replacement
 Samples obtained from table of random
numbers or computer random number
generators
Stratified Samples
 Population divided into two or more groups
according to some common characteristic
 Simple random sample selected from each
group
 The two or more samples are combined into
one
Stratified Sampling Example
Population
Cash holdings of
All Financial
Institutions in the
United States
Financial Institutions
Stratified Population
Stratum 1
Large Institutions
Select n1
Stratum 2
Medium Size Institutions
Select n2
Stratum 3
Small Institutions
Select n3
Cluster Samples
 Population divided into several “clusters,” each
representative of the population
 Randomly select certain clusters
 The samples are combined into one
Population
divided
into 4
clusters.
Cluster Sampling Example
Mid-Level Managers by Location for Morrison-Knudsen
Construction Company
Algeria
25
Illinois Scotland California
42
22
105
Alaska New York Florida
20
36
52
Idaho
152
Mexico Australia
76
37
Cluster Sampling Example
Mid-Level Managers by Location for Morrison-Knudsen
Construction Company
Illinois Scotland
42
22
Florida
52
All members selected from these clusters
Types of Survey Errors
 Coverage error
Excluded from
frame.
 Non response error
Follow up on
non responses.
 Sampling error
 Measurement error
Chance
differences from
sample to sample.
Bad Question!
II. Survey Contents
 Remember that your respondents will be
“Lazy Thinkers.”
Survey Contents
 When creating questions, consider the effects
of the following elements:
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Type
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Wording
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Order
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Content
Survey Contents: Type
 Open-ended
A survey question to which
the respondent replies in
his or her own words,
either by writing or by
talking
 difficult to analyze,
subjective analysis
 time consuming
 rich information
 useful for descriptive,
exploratory work
 Closed-ended or fixed-
choice
A survey question that
provides preformatted
response choices for the
respondent to circle,
check, mark, etc.
 easier to analyze
 efficient
 useful for hypothesis
testing
 important info may be
lost forever
Closed-ended Questions
 Closed-ended or fixed-choice
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Response options are limited
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Yes/no
True/false
Multiple choice with an “other” option
 Race: White, Black, Hispanic, Asian, Other
Likert Scales
1
2
3
4
5
Strongly Agree Neither Disagree Strongly
Agree
A nor D
Disagree
Rating Scales
Ask respondents to rate something like a person, place, thing, idea,
attitude, etc. on a numbered scale, often Likert scales
 Semantic Differential
a fifth grader is
Bad
Good
Awful ⊲
⊲ ⊲ ⊲  ⊳ ⊳ ⊳
⊳ Nice
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Survey Contents: Wording
 Guidelines for good questions:
1.
2.
3.
4.
Be direct
Maintain simplicity
Be specific
Take the role of your respondent
The following points elaborate on these four main
themes.
Survey Contents: Wording
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Respondents should understand your questions. No
complex rhetoric, syntax, or disciplinary slang or jargon.
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Pre-testing is a very effective way to see if they do
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Do not expect them to learn new information just
answer a question. (Sometimes, you may establish
context with a short paragraph then ask a series of
short, specific questions.)
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Avoid ambiguous questions.
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“Do you teach your children to effectively function?” “Does your
boss engage you in interactive dialogue?” “Effectively function”
and “interactive dialogue” are subject to interpretation.
Words such as "usually" or "normally" mean different things to
different people. “Do your customers normally complain?” has a
variety of interpretations.
Survey Contents: Wording
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Avoid Double-barreled questions. They contain two questions
in one. For example, “Do you think that students and
Professors should be given discounts on sports tickets?”
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Avoid Double-negative questions. For example, “Do you
disagree that professors should not be required to help
students outside of class?”
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Avoid loaded questions. Avoid making one response option
look more suitable than the other, using emotionally loaded
terms, or using unbalanced response categories.
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“Don’t you think that suffering terminal cancer patients should be allowed
to be released from their pain by choosing death?”
Virginia pays teachers more than similar states. Virginia should: spend
more, keep spending the same, reduce spending little, reduce spending
some, reduce spending a lot, dramatically reduce spending
Survey Contents: Order
Relative placement of questions in the
instrument
 Opening questions should be simple and introduce the
topic of the survey. Also put most important questions
early.
 Put closed-ended questions early in the survey and
open-ended questions later.
 Avoid a lot of “skipping” or “go to next section”. R’s will
get confused/frustrated.
Survey Contents: Order
 Try not to mix topics. Put like things into sets of
questions. Clearly transition between types of questions.
 Sensitive questions should never be at the beginning.
Put in middle. May need opening paragraph for them.
 Avoid framing later questions with topics that can be
linked to them in previous questions. For example, one
should not ask about attitudes toward crack use right
before asking about attitudes toward the urban poor.
This may invoke stereotypes about the poor.
Survey Contents: Content
Topics the questions cover
 You should make the topic of the survey clear to R’s. Do not
surprise them with questions about unrelated topics.
 If including sensitive questions, provide a rationale for asking
them. Explain how honest answers will be helpful to others
and reassure confidentiality.
 Questions relevant to deviance should include normalizing
statements. For example, “Many people use drugs for a
variety of reasons. Have you ever used ecstasy (or x, e,
MDMA) to feel closer to other people?”
 Questions that require lots of specific details or a good
memory are typically useless. If they are necessary, employ
techniques to prompt recollection.
Survey Contents
 General Advice
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Always consult other surveys first
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Always pre-test your instrument
 Consider these issues:
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Consider “no opinion” as an option.
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People want to appear to agree. Consider negative and
positive statements.
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R’s may lose track and choose salient options (such as first
in series). Keep questions simple.
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Response set problem
Survey Contents
 Consider these issues:
 Bad memory leads to:
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Forward telescoping (reporting that events occurred
more recently than in reality)
Backward telescoping (reporting events further back
than in reality).
Salient events are overreported
Mundane events are underreported
“Habitual” events will fill in for lost information.
Provide aides to recall such as reference points,
landmark events, etc. Use limited time frames in
questions.
Class Exercise
 Split into groups
 Select a topic for a survey
 Develop 2 closed-ended and 2 open-ended
questions. For each question, write a ‘poor’
version and a ‘good’ version
 Administer the survey to member of another
group. Critique each other’s questions