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Example 4

A Detailed Example of Construct Validation

The Inflammatory Bowel Disease Questionnaire (IBDQ) was designed to measure disease-specific HRQL and it includes 30 items directed at 4 domains: bowel symptoms, systemic symptoms, emotional function, and so­cial function. Investigators administered the IBDQ (along with global ratings of change in function, global ratings of change by the physician and a relative, a Disease Activity In­dex, and the emotional function domain of a generic HRQL measure) to 42 patients with inflammatory bowel disease on two occasions separated by 1 month. At the time the investigation was planned, the investigators made predictions about how change in the IBDQ score should relate to change in the other measures if this questionnaire was really measuring HRQL. Examples of the predictions and the results are as follows:

  • The patient's global rating of change in disease activity should relate closely (correlation ~ 0.5) with change in the bowel-symptoms dimension of the In­flammatory Bowel Disease Questionnaire.
    Correlation observed was 0.42.
  • Some relation (correlation ~ 0.3) should exist between change in the Disease Activity Index and change in the bowel-symptoms dimension of the In­flammatory Bowel Disease Questionnaire.
    Correlation observed was 0.33.
  • Some relation (correlation ~ 0.3) should exist between change in the Disease Activity Index and change in the systemic-symptoms dimension of the Inflammatory Bowel Disease Questionnaire.
    Correla­tion observed was 0.04.
  • Change in the emotional-function dimension of the Inflammatory Bowel Disease Questionnaire should relate closely (correlation ~ 0.5) with change in the emotional-function dimension of the generic questionnaire.
    Correlation observed was 0.76.
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