Survey Research

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Survey Research Understanding Statistics
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Central Tendency
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Measures of Central Tendency
Central Tendency
Average (Mean)
Median
Mode
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Mean (Arithmetic Mean)

• Mean (arithmetic mean) of data values
• Sample mean

Sample Size
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Mean

• The most common measure of central tendency
• Affected by extreme values (outliers)

0 1 2 3 4 5 6 7 8 9 10
0 1 2 3 4 5 6 7 8 9 10 12
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Mean 5
Mean 6
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Median

• Robust measure of central tendency
• Not affected by extreme values
• Median is the middle number

0 1 2 3 4 5 6 7 8 9 10
0 1 2 3 4 5 6 7 8 9 10 12
14
Median 5
Median 5
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Mode

• A measure of central tendency
• Value that occurs most often
• Not affected by extreme values
• Used for either numerical or categorical data
• There may may be no mode
• There may be several modes

0 1 2 3 4 5 6
0 1 2 3 4 5 6 7 8 9 10 11
12 13 14
No Mode
Mode 9
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Survey Research
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What is a Survey?

• Researchers are often interested in the opinions
  of a large group of people about a particular
  topic or issue.
• There are three major characteristics that most
  surveys possess
• Information is collected from a group of people
  in order to describe some aspect of the
  population
• Information is collected by asking questions of
  the members of the selected group
• Information is collected from a sample rather
  than from every member of the population

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Question

• What are common problems with survey research?

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Why Are Surveys Conducted?

• The purpose of surveys is to describe the
  characteristics of a population.
• Researchers find out how the members of a
  population distribute themselves on one or more
  variables.
• A selected sample is surveyed and the description
  of the population is inferred from what is found
  out about the sample.
• In descriptive surveys, researchers are not as
  concerned about why the observed distribution
  exists as with what the distribution is.

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Types of Surveys

• There are two types of surveys
• Cross-sectional survey
• Collects information from a sample that has been
  drawn from a predetermined population
• Information is collected at just one point in
  time, even though it could take days to gather
  all the data
• A census is when the entire population is
  surveyed
• Longitudinal survey
• Information is collected at different points in
  time in order to study changes over time
• Three types are employed
• Trend study
• Cohort Study
• Panel Study

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Survey Research and Correlational Research

• Techniques of Correlational Research can be tied
  in with Survey Research.
• Researchers could look at the relationship of
  responses to one question (survey) to another, or
  of a score based on one set of questions to
  another set.
• The use of calculating correlation coefficients
  or contingency tables could be determined and
  implemented.

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Steps in Survey Research

• The following steps are used in conjunction with
  performing proper surveys in research
• Defining the problem
• Identifying the target population (unit of
  analysis)
• Choosing the mode of data collection
• Direct administration
• Mail surveys
• Telephone surveys
• Personal interviews

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Example of an Ideal vs. an Actual Telephone
Sample for a Specific Question
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Steps in Survey Research(cont.)

• The following steps are used in conjunction with
  performing proper surveys in research
• Selecting the sample
• Preparing the instrument (questionnaire)
• Closed-ended questions
• Open-ended questions
• Pre-testing the questionnaire
• Format
• Cover letter
• Training interviewers

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Example of Contingency Questions
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Non-response

• In almost all surveys, some members of the sample
  will not respond.
• Item non-response is due to unclear or
  questionable forms of wording.
• Non-response is a serious problem in many
  surveys.
• A variety of techniques are employed to reduce
  this problem (e.g., rewards or incentive for
  completing the surveys).

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Data Analysis in Survey Research

• After researchers receive the completed
  questionnaires, the task of summarizing the
  results remains.
• The total size of the sample and total percentage
  of returns should be reported.
• The percentage of the total sample responding for
  each item should be reported.
• The percentage of respondents who chose each
  alternative for each question should be given.

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Variability
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Shapes of Distributions

• Normal distribution
• Positive Skew
• Or right skewed
• Negative Skew
• Or left skewed

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How is this variable distributed?
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How is this variable distributed?
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How is this variable distributed?
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Standard Deviation

• Considered the most useful index of variability.
• It is a single number that represents the spread
  of a distribution.
• If a distribution is normal, then the mean plus
  or minus 3 SD will encompass about 99 of all
  scores in the distribution.

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Comparing Standard Deviations
Data A
Mean 15.5 S 3.338
11 12 13 14 15 16 17 18
19 20 21
Data B
Mean 15.5 S .9258
11 12 13 14 15 16 17 18
19 20 21
Data C
Mean 15.5 S 4.57
11 12 13 14 15 16 17 18
19 20 21
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Facts about the Normal Distribution

• 50 of all the observations fall on each side of
  the mean.
• 68 of scores fall within 1 SD of the mean in a
  normal distribution.
• 27 of the observations fall between 1 and 2 SD
  from the mean.
• 99.7 of all scores fall within 3 SD of the mean.
  
• This is often referred to as the 68-95-99.7 rule

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Fifty Percent of All Scores in a Normal Curve
Fall on Each Side of the Mean
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Probabilities Under the Normal Curve
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The Importance of Converging Evidence

• The connectivity principle
• New theory in science must make contact with
  established facts.
• Beware of violations of connectivity.
• Converging evidence
• Single studies have flaws
• Together the flaws should wash out.
• When might this not be true?

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Meta-Analysis

• A meta-analysis is a statistical procedure when
  the researcher averages the results of a group of
  selected studies to get an overall index of
  outcome or relationship.

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Experimental vs. Nonexperimental

• Experiments
• Treatment is administered
• Students divided into two groups one group
  receives new reading materials the other uses the
  traditional materials.
• Cancer patients are divided into two groups one
  group receives a new drug the other receives the
  current treatment of choice.
• Nonexperiments
• No manipulation of treatment present
• Individuals given a survey asking about
  television viewing habits.
• Classrooms observed to see if teachers
  expectations affect student performance.

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Correlational

• Study Relationships
• SAT and Achievement
• Income and achievement
• Age and Cholesterol level

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Causal-Comparative Studies.

• Causal-comparative (a.k.a. ex post facto)
• Two characteristics
• Observe and describe a current condition
• Look to the past, or demographic characteristics,
  to identify a cause.

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Survey Research

• Used to describe
• Attitudes
• Opinions
• Beliefs
• Behaviors
• Usually include large numbers