QUALITY OF LIFE IN PSORIASIS PATIENTS. VALIDATION OF THE PORTUGUESE VERSION OF THE PSORIASIS DISABILITY INDEX

Abstract

Introduction: The authors describe the process of translation, cultural adaption and validation of the instrument for measuring quality of life of patients with psoriasis PDI (Psoriasis Disability Index).

Methods: This questionnaire comprises 15 questions concerning the last four weeks, divided into five chapters; daily activities, work or school, personal relationships, leisure activities and treatment. The questionnaire was translated according to the standards for cross-cultural validation of health outcomes instruments.

Results: In a sample of 171 patients aged between 16 and 82 years, 61,9% were male. Content validity was assured by a cognitive debriefing and the reliability was verified by a reproducibility test (r=0,888) and by internal consistency (α=0,857). Criterion validity was tested by comparing PDI results with those obtai- ned by PASI, and there has been a positive correlation (p<0,05) in all dimensions of the questionnaire.

Conclusions: We can defend the performance quality of the Portuguese version of the PDI. The study of psychometric characteristics of PDI allows the use of this instrument for the Portuguese population, either in research or in clinical practice. There remains, however, the need to obtain values of clinical significance and national reference standards.

KEYWORDS – Quality of life; Psoriasis; Questionnaires.