The reduced Impact of Psoriasis Questionnaire has good psychometric properties in Italian patients.

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.