Applying Item Response Theory to the OPD Structure Questionnaire: Identification of a Unidimensional Core Construct and Feasibility of Computer Adaptive Testing

Abstract

Recent developments in the dimensional assessment of personality functioning have made the implementation of latent measurement models increasingly attractive. In this study, we applied item response theory (IRT) to a well-established personality functioning instrument (the OPD Structure Questionnaire) to identify a unidimensional latent trait and to evaluate the feasibility of computer adaptive testing (CAT). We hypothesized that the use of IRT could reduce the test bur- den – compared to a fixed short form – while maintaining high precision over a wide range of the latent trait. The OPD-SQ was collected from 1235 patients in a psychosomatic clinic. IRT assumptions were fulfilled. A 9-factor model yielded sufficient fit and unidimensionality in explora- tory factor analysis with bifactor rotation. Items were iteratively reduced, and a graded-response IRT model was fitted to the data. Simulations showed that a CAT with approximately 7 items was able to capture an OPD-SQ global severity score with an accuracy similar to that of a fixed 12- item short form. The final item bank and CAT yielded satisfactory content validity. Strong correlations with depression and anxiety replicated previous results on the OPD-SQ. We concluded that IRT applications could be useful to reduce the test burden of personality functioning instruments.

Publication
Journal of Personality Assessment
Alexander Obbarius
Alexander Obbarius
Psychometrics and Health Outcomes
Felix Fischer
Felix Fischer
Group Leader Psychometrics and Health Outcomes

Psychologist with a weakness for quantitative data analysis

Gregor Liegl
Gregor Liegl
Psychometrics and Health Outcomes
Nina Obbarius
Nina Obbarius
Psychometrics and Health Outcomes
Matthias Rose
Matthias Rose
Department Head

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