Abstract
In order to develop a psoriasis specific, health-related QOL (quality of life) index in Japan, we developed a Japanese version of the Psoriasis Disability Index (Japanese PDI) and examined its reliability and validity by examining its relevance to the comprehensive health-related QOL index, SF-36 (short form-36). In creating the Japanese PDI, we first made a draft which adhered to general methods of QOL questionnaire development and completed it using a feasibility study with 5 psoriasis patients. We conducted a validation study in 200 psoriasis patients to examine its reliability, validity and responsiveness ; they responded to both the Japanese PDI and the SF-36. It took about 2 minutes to complete the Japanese PDI. The missing value (unanswered) rate for each of the 15 question categories of the Japanese PDI questionnaire was below 10%. The questionnaire shows good reliability with Cronbach’s coefficient alpha at 0.910. In factor analysis, eigen values were high (>1.0) for factors explaining“leisure/treatment,” “work/school,” “daily activities,” and “personal relationships.” A sufficient correlation coefficient of –0.547 was shown between the total PDI score and the SF-36. In conclusion, the newly developed Japanese PDI has sufficient reliability and validity to evaluate health-related QOL in Japanese psoriasis patients.
