Abstract
PurposeMany paper-and-pencil (P&P) questionnaires have been migrated to electronic platforms. Differential item and test functioning (DIF and DTF) analysis constitutes a superior research design to assess measurement equivalence across modes of administration. The purpose of this study was to demonstrate an item response theory (IRT)-based DIF and DTF analysis to assess the measurement equivalence of a Web-based version and the original P&P format of the Four-Dimensional Symptom Questionnaire (4DSQ), measuring distress, depression, anxiety, and somatization.MethodsThe P&P group (n = 2031) and the Web group (n = 958) consisted of primary care psychology clients. Unidimensionality and local independence of the 4DSQ scales were examined using IRT and Yen’s Q3. Bifactor modeling was used to assess the scales’ essential unidimensionality. Measurement equivalence was assessed using IRT-based DIF analysis using a 3-stage approach: linking on the latent mean and variance, selection of anchor items, and DIF testing using the Wald test. DTF was evaluated by comparing expected scale scores as a function of the latent trait.ResultsThe 4DSQ scales proved to be essentially unidimensional in both modalities. Five items, belonging to the distress and somatization scales, displayed small amounts of DIF. DTF analysis revealed that the impact of DIF on the scale level was negligible.ConclusionsIRT-based DIF and DTF analysis is demonstrated as a way to assess the equivalence of Web-based and P&P questionnaire modalities. Data obtained with the Web-based 4DSQ are equivalent to data obtained with the P&P version.
Highlights
Many questionnaires have been developed and validated as paper-and-pencil (P&P) questionnaires
It is recommended that measurement equivalence between a Web-based questionnaire and the original P&P questionnaire be supported by appropriate evidence [2]
We demonstrate the use of differential item functioning (DIF) analysis within the item response theory (IRT) framework by assessing measurement equivalence across a Web-based and the original P&P versions of the Four-Dimensional Symptom Questionnaire (4DSQ)
Summary
Many questionnaires have been developed and validated as paper-and-pencil (P&P) questionnaires. It is recommended that measurement equivalence between a Web-based questionnaire and the original P&P questionnaire be supported by appropriate evidence [2] Four reviews of such equivalence studies suggested that, in most instances, electronic questionnaires and P&P questionnaires produce equivalent results [3,4,5,6]. We will demonstrate the use of modern psychometric methods to assess the equivalence across two modalities of a questionnaire. This is illustrated by analyzing the Web-based and P&P versions of the Four-Dimensional Symptom Questionnaire (4DSQ), a self-report questionnaire measuring distress, depression, anxiety, and somatization
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