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Assessment. 2015 Aug;22(4):513-24. doi: 10.1177/1073191114560882. Epub 2014 Dec 16.

Detecting and Explaining Aberrant Responding to the Outcome Questionnaire-45.

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School of Social and Behavioral Sciences, Tilburg University, Tilburg, Netherlands
School of Social and Behavioral Sciences, Tilburg University, Tilburg, Netherlands.
Institute of Psychology, Leiden University, Leiden, Netherlands Research department, GGZ Noord-Holland-Noord.


We applied item response theory based person-fit analysis (PFA) to data of the Outcome Questionnaire-45 (OQ-45) to investigate the prevalence and causes of aberrant responding in a sample of Dutch clinical outpatients. The [Formula: see text] person-fit statistic was used to detect misfitting item-score patterns and the standardized residual statistic for identifying the source of the misfit in the item-score patterns identified as misfitting. Logistic regression analysis was used to predict person misfit from clinical diagnosis, OQ-45 total score, and Global Assessment of Functioning code. The [Formula: see text] statistic classified 12.6% of the item-score patterns as misfitting. Person misfit was positively related to the severity of psychological distress. Furthermore, patients with psychotic disorders, somatoform disorders, or substance-related disorders more likely showed misfit than the baseline group of patients with mood and anxiety disorders. The results suggest that general outcome measures such as the OQ-45 are not equally appropriate for patients with different disorders. Our study emphasizes the importance of person-misfit detection in clinical practice.


Outcome Questionnaire–45; aberrant responding; item response theory; outcome measurement; person-fit analysis

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