Developing a quality of life instrument in patients with psoriasis:: the Psoriasis Quality of Life Questionnaire (PQLQ)

Background and design Psoriasis is a chronic skin disease which causes psychological, social and physical problems and affects quality of life. The aim of this study was to develop a quality of life instrument for patients with psoriasis which is suitable for Islamic populations. Materials and methods The psychosocial and daily life problems defined by 75 patients with psoriasis, their relatives and physicians were used to construct a questionnaire, the reliability and validity of which were determined in a group of 156 patients with psoriasis. Results For reliability, Chronbach's alpha coefficient was 0.87, and item-total correlations were between 0.37 and 0.60 for internal consistency. There was high test-retest reliability (r = 0.98, P < 0.001). For validity, three factors were extracted in the principal components method for construct validity. The maximum factor loadings of each item were between 0.456 and 0.681. For convergent validity, all patients' self-ratings and Psoriasis Area and Severity Index (PASI) were correlated with the questionnaire score (P < 0.001). Conclusions The questionnaire consisting of 17 items was found to be suitable for both epidemiologic and clinical trials.