Discriminant content validity: A quantitative methodology for assessing content of theory‐based measures, with illustrative applications

Abstract

The DCV method allowed quantitative assessment of each item and can therefore inform the content validity of the measures assessed. The methods can be applied to assess content validity before or after collecting data to select the appropriate items to measure theoretical constructs. Further, the data reported for each item in Appendix S1 can be used in item or measure selection. Statement of contribution What is already known on this subject? There are agreed methods of assessing and reporting construct validity of measures of theoretical constructs, but not their content validity. Content validity is rarely reported in a systematic and transparent manner. What does this study add? The paper proposes discriminant content validity (DCV), a systematic and transparent method of assessing and reporting whether items assess the intended theoretical construct and only that construct. In three studies, DCV was applied to measures of illness perceptions, control cognitions, and theory of planned behaviour response formats. Appendix S1 gives content validity indices for each item of each questionnaire investigated. Discriminant content validity is ideally applied while the measure is being developed, before using to measure the construct(s), but can also be applied after using a measure.