Application of the Rasch model in measuring personality disorders.

OBJECTIVE To describe item and person parameters obtained with the Rasch model, one of the item response theory models, in the assessment of personality disorders based on Millon's theory. METHOD A total of 350 people participated in the study. Age ranged from 18 to 67 years (mean ± standard deviation = 27.02±10.13), and 71.7% of the participants (n = 251) were female. Of the 350 individuals, 21.1% (n = 74) answered affirmatively about being under psychiatric treatment and taking psychiatric medications. The Personality Disorders Dimensional Inventory (PDDI), an instrument designed to assess personality disorders according to Millon's theory, was applied to all participants. Data were analyzed using the Rasch model. RESULTS Overall, analysis with the Rasch model revealed that the PDDI has adequate psychometric properties for the assessment of personality disorders. CONCLUSION Among the contributions of item response theory models for clinical instruments, the Rasch person-item map deserves to be highlighted as a successful attempt to improve the understanding of clinical scores obtained in response to particular test items.