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Related Experiment Videos

Questionnaire discrimination: (re)-introducing coefficient delta.

Matthew Hankins1

  • 1King's College London, Department of Psychology (at Guy's), Institute of Psychiatry, London, UK. matthew.hankins@kcl.ac.uk

BMC Medical Research Methodology
|May 22, 2007
PubMed
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A new index, deltaG, enhances questionnaire discrimination by distinguishing between individuals. This method is more effective than traditional reliability and validity measures for assessing how well questionnaires differentiate people.

Area of Science:

  • Psychometrics
  • Health Services Research
  • Statistical Modeling

Background:

  • Questionnaires are vital for measuring health status and quality of life in clinical research.
  • Traditional assessments focus on reliability and validity, neglecting a questionnaire's ability to discriminate between individuals.
  • Discrimination is a crucial, yet often overlooked, aspect of questionnaire measurement.

Purpose of the Study:

  • To introduce and extend an existing index for measuring a questionnaire's discrimination ability.
  • To derive a generalized formula (deltaG) for questionnaires with multiple response choices.
  • To compare the discrimination of dichotomous versus Likert-type coding using the deltaG index.

Main Methods:

  • Derived a generalized discrimination index, deltaG, extending Ferguson's coefficient delta for polytomous items.

Related Experiment Videos

  • Applied deltaG and reliability (alpha) calculations to the GHQ-12 questionnaire using British Household Panel Survey data (N=14761).
  • Compared deltaG values for dichotomous and four-point Likert-type coding of the GHQ-12.

    • Main Results:

    • Both dichotomous and Likert-type coding of GHQ-12 demonstrated high reliability (alpha > 0.88).
    • The Likert-type coding (deltaG = 0.96) showed substantially higher discrimination than dichotomous coding (deltaG = 0.73).
    • Results indicate that dichotomous coding, despite reliability, poorly discriminates between individuals.

    Conclusions:

    • The deltaG index effectively distinguishes the cross-sectional discrimination of different scoring methods, even with equal reliability.
    • The generalized deltaG formula addresses limitations of Ferguson's delta, making it applicable to diverse health questionnaires.
    • Reporting deltaG is recommended to accurately reflect a questionnaire's discriminative performance beyond simple reliability.