In search of content validity: facet analysis as a qualitative method to improve questionnaire design

In this paper, two scales are examined for the measurement of self-regulation. The item content is evaluated for its specific usefulness for measuring self-regulation of obesity patients. Qualitative facet analysis (QFA), an application of Guttmann’s Facet Theory, is used to investigate whether item content sufficiently covers the intended content area. This form of content analysis constitutes a systematic, effective and critical tool for improving the content validity of questionnaires. It discovers topics that are underrepresented or overrepresented. The method offers a way to clarify the relationship between concrete item phrases and the desired content as defined by construct and theory. It allows the researcher to improve his or her understanding of the items as a stimulus and of the similarities of items, and allows the formulation of a possible structure for confirmative factor analysis. Various ways to improve the content of both scales are identified.