Retrospective Pretesting Post then Pre

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Retrospective Pre-testingPost - then - Pre

• Extension Educators oft times use the Pre and
  Post test design to determine if there is any
  differences (changes of attitudes or behaviors)
  following the delivery of a program

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Problems with Pre- Post Testing

• Pre-tests taken at the beginning of the program
  my be invalid because participants have limited
  knowledge in responding accurately to questions
  in the pre-test.
• Do you include one food rich in vitamin C in your
  diet daily?
• If participant doesnt know which foods are rich
  in vitamin C they may overestimate vitamin C on
  the pretest.

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Problems with Pre- Post Testing

• After participating in the Extension Program and
  learning which foods are rich in vitamin C the
  participant can validly answer the question.
• On the post test (aimed at measuring change
  in behavior) the participant indicates that they
  increased their vitamin C intake as a result of
  the program. If participant over estimated their
  vitamin C intake in the pre-test and then
  reported they increased intake on the posttest
  the amount of change will appear to be no
  change at all since levels were inaccurately
  estimated in the pre-test. The program had no
  effect! ???

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Post - then - Pre Test Design
Post
Pre

• Now Then

Think _________
How You Felt AFTER the Program
How you felt BEFORE the Program
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Example of Post - then - Pre

• Rate your knowledge about SURVEY TECHNIQUES on
  the scale below. Place the letter N on the
  scale where you rate your knowledge NOW at the
  end of todays program. Place the letter B on
  the scale where you would rate your knowledge
  BEFORE todays program.
• 1 2 3 4 5 6 7 8 9 10
• Low High

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Statistical Analysis

• Use Students Paired t test to analyze the mean
  differences in the participants test with the
  before and now scale.
• A t statistic is calculated to determine if
  there is a significant difference in the group
  means before and now. Differences can potentially
  be reported as changes in behavior, attitude,
  attributes or beliefs. K Rockwell,
  University of Nebraska

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For Further Information Contact

• Dr Dallas L. Holmes
• Utah State University Extension
• Specialist
• Institutional Research
• DallasH_at_Ext.USU.EDU
• [phone]