![]() ![]() ![]() ![]() The presentations were diverse: from an introduction to IRT to examples of Rasch models and Mokken scale analyses. The 4th Methods in Health Psychology symposium at the EHPS in Innsbruck was organised by Alexandra Dima (University of Amsterdam), who together with Chris Gibbons (University of Manchester), Mieke Kleppe (Phillips Research and Eindhoven University of Technology), and Katarzyna Byrka (University of Social Sciences and Humanities of Wroclaw) organised an excellent and inspiring symposium on using Item Response Theory for developing and validating questionnaires and theory testing. The outcomes of all three approaches substantiate the conviction that the assessment of dimensionality requires a good deal of judgment. TETRAD successfully confirmed one dimension in the single-construct data set and was able to confirm two dimensions in the combined data set, yet excluded one item from each cluster, for no obvious reasons. Parallel Analysis successfully identified the correct number of factors and while the Rasch approach did not show the item misfit that would indicate deviation from clear unidimensionality, the pattern of residuals did seem to indicate the presence of correlated, yet distinct, factors. The three methods were all found to be reasonably effective. In this study, we employ polytomous item responses to compare two methods that have received increased attention in recent years (Rasch model and Parallel analysis) with a method for evaluating assessment structure that is less well-known in the educational measurement community (TETRAD). The evaluation of assessment dimensionality is a necessary stage in the gathering of evidence to support the validity of interpretations based on a total score, particularly when assessment development and analysis are conducted within an item response theory (IRT) framework. ![]()
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