Chapter 1 Section 4

1
Chapter 1Section 4

• Sources of Error
• In Sampling

2
Chapter 1 Section 4

• One type of error, sampling errors, occur because
  we use only part of the population in our study

• One type of error, sampling errors, occur because
  we use only part of the population in our study
• Samples consist of only part of the total data

• One type of error, sampling errors, occur because
  we use only part of the population in our study
• Samples consist of only part of the total data
• Samples are usually more realistic to analyze

• One type of error, sampling errors, occur because
  we use only part of the population in our study
• Samples consist of only part of the total data
• Samples are usually more realistic to analyze
• Because there are individuals in the population
  that are not in our sample, sampling errors are
  difficult to control

• One type of error, sampling errors, occur because
  we use only part of the population in our study
• Samples consist of only part of the total data
• Samples are usually more realistic to analyze
• Because there are individuals in the population
  that are not in our sample, sampling errors are
  difficult to control
• We will study sampling errors in future chapters

3
Chapter 1 Section 4

• Another type of error, nonsampling errors, occur
  from the actual survey process
• Preference is given to selecting some individuals
  over others
• Individual answers are not accurate (for various
  reasons)
• Nonsampling errors can often be controlled or
  minimized with a well-designed survey and
  sampling technique

4
Chapter 1 Section 4

• Types of nonsampling error

• Types of nonsampling error
• Using an incomplete frame

• Types of nonsampling error
• Using an incomplete frame
• Individuals who respond have different
  characteristics than individuals who do not
  respond

• Types of nonsampling error
• Using an incomplete frame
• Individuals who respond have different
  characteristics than individuals who do not
  respond
• Interviewer errors

• Types of nonsampling error
• Using an incomplete frame
• Individuals who respond have different
  characteristics than individuals who do not
  respond
• Interviewer errors
• Misrepresented answers

• Types of nonsampling error
• Using an incomplete frame
• Individuals who respond have different
  characteristics than individuals who do not
  respond
• Interviewer errors
• Misrepresented answers
• Data checks

• Types of nonsampling error
• Using an incomplete frame
• Individuals who respond have different
  characteristics than individuals who do not
  respond
• Interviewer errors
• Misrepresented answers
• Data checks
• Questionnaire design

• Types of nonsampling error
• Using an incomplete frame
• Individuals who respond have different
  characteristics than individuals who do not
  respond
• Interviewer errors
• Misrepresented answers
• Data checks
• Questionnaire design
• Wording of questions

• Types of nonsampling error
• Using an incomplete frame
• Individuals who respond have different
  characteristics than individuals who do not
  respond
• Interviewer errors
• Misrepresented answers
• Data checks
• Questionnaire design
• Wording of questions
• Order of questions, words, and responses

5
Chapter 1 Section 4

• The Literary Digest used their polls to predict
  the winner of presidential elections

• The Literary Digest used their polls to predict
  the winner of presidential elections
• Their previous polls were accurate

• The Literary Digest used their polls to predict
  the winner of presidential elections
• Their previous polls were accurate
• In 1936, the Literary Digest predicted that Alf
  Landon would defeat Franklin Roosevelt in a
  landslide

• The Literary Digest used their polls to predict
  the winner of presidential elections
• Their previous polls were accurate
• In 1936, the Literary Digest predicted that Alf
  Landon would defeat Franklin Roosevelt in a
  landslide
• In the actual election, Roosevelt won in a
  landslide

6
Chapter 1 Section 4

• Why was the Literary Digest so far off?
• The 1936 frame was not representative of the
  total voting population

• Why was the Literary Digest so far off?
• The 1936 frame was not representative of the
  total voting population
• The sampling process was not completely random

• Why was the Literary Digest so far off?
• The 1936 frame was not representative of the
  total voting population
• The sampling process was not completely random
• The frame had too large of a proportion of
  Republicans, who generally favored Landon

• Why was the Literary Digest so far off?
• The 1936 frame was not representative of the
  total voting population
• The sampling process was not completely random
• The frame had too large of a proportion of
  Republicans, who generally favored Landon
• The frame had too small of a proportion of
  Democrats, who generally favored Roosevelt

• Why was the Literary Digest so far off?
• The 1936 frame was not representative of the
  total voting population
• The sampling process was not completely random
• The frame had too large of a proportion of
  Republicans, who generally favored Landon
• The frame had too small of a proportion of
  Democrats, who generally favored Roosevelt
• Republicans were overrepresented and Democrats
  were underrepresented

7
Chapter 1 Section 4

• Interviewer errors may occur when
• The interviewer has a vested interest in the
  results

• Interviewer errors may occur when
• The interviewer has a vested interest in the
  results
• The interviewer is not trained to obtain accurate
  information

• Interviewer errors may occur when
• The interviewer has a vested interest in the
  results
• The interviewer is not trained to obtain accurate
  information
• The individuals feel pressure or an obligation to
  provide an answer that the interviewer desires

• Interviewer errors may occur when
• The interviewer has a vested interest in the
  results
• The interviewer is not trained to obtain accurate
  information
• The individuals feel pressure or an obligation to
  provide an answer that the interviewer desires
• For example, if your server watches you when you
  fill out the restaurants service satisfaction
  questionnaire

8
Chapter 1 Section 4

• Some individuals may deliberately lie in their
  responses
• Even if the other aspects of the survey are
  designed well, the individual may want to look
  good or may be embarrassed about giving truthful
  answers

9
Chapter 1 Section 4

• Data recorded by the individuals may be entered
  incorrectly onto the questionnaire
• Data recorded by hand can often be entered into
  the system incorrectly (typos)
• There are some techniques for detecting these
  errors, such as examining outliers

10
Chapter 1 Section 4

• Wording of questions could affect the accuracy of
  responses
• Some questions are not asked in balanced form
• Some questions are worded in confusing ways
• Some questions are too vague

• Wording of questions could affect the accuracy of
  responses
• Some questions are not asked in balanced form
• Some questions are worded in confusing ways
• Some questions are too vague
• The same question, worded in two different
  confusing ways, could result in two different
  results

11
Summary Chapter 1 Section 4

• There are reasons why samples have errors
• Sampling errors are difficult to control because
  we use only part of the total population
• Nonsampling errors are often largely avoidable
  with a good study design
• Minimizing nonsampling errors is of high priority
  in designing a sample survey