Background: A recent refinement study suggested that a Rasch reduced version of the Impact of Psoriasis Questionnaire (IPSO) of 11 items most adequately assessed the psychosocial impact of US psoriasis patients. Objective: To test whether the IPSO would also behave well in a different population that varies culturally, demographically, and in disease severity. Methods: The psychometric properties of the IPSO, using classical test and item response theory (Rasch analysis), were assessed in 805 Italian psoriasis patients. Results: Patients with more severe psoriasis reported significantly higher impact on their HRQOL (p < 0.001) and the IPSO correlated well with the Skindex-29 (r = 0.74) confirming its validity. The response distribution was adequate for all items, except item 9. The Cronbach's alphas were excellent and the high item-rest correlations confirmed its homogeneity. Principal component analysis demonstrated one dominant factor with an eigenvalue of 4.47 (items loading >0.40). Overall, the 11 IPSO items fitted the Rasch model (p = 0.07) and all items demonstrated a logical threshold order. Of the 11 items, 2 items showed significant individual misfit and only 1 item demonstrated significant differential item functioning for age but none for gender or global severity score. Conclusion: The 11-item IPSO is a valuable psoriasis-specific HRQOL instrument in different populations. Copyright

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Dermatology: international journal for clinical and investigative dermatology
Erasmus MC: University Medical Center Rotterdam

Nijsten, T., Sampogna, F., Stern, R., & Abeni, D. (2007). The reduced Impact of Psoriasis Questionnaire has good psychometric properties in Italian patients. Dermatology: international journal for clinical and investigative dermatology, 215(4), 348–351. doi:10.1159/000107629