Qualitative assessment of the content validity of the Dermatology Life Quality Index in patients with moderate to severe psoriasis

Background: The patient-reported Dermatology Life Quality Index (DLQI) measures the impact of dermatologic diseases on patients' lives. Objectives: To evaluate the content validity of the DLQI in patients with moderate to severe plaque psoriasis. Methods: In a two-part interview, participants were first asked open-ended questions about the impact of psoriasis-related complaints and symptoms on their lives and activities. The DLQI was then administered and cognitive debriefing interviews assessed participants' understanding of the instructions, items, and response scales, and relevance of the specific items to their experience with psoriasis. Results: Twenty-one patients were interviewed at two US sites. Mean age was 48.8 years, 67% were white, and 43% reported Hispanic/Latino ethnicity. The majority reported living with a partner or spouse (81%) and working full time or part time (57%). Patients' spontaneous responses to open-ended questions were consistent with DLQI concepts and generally did not provide additional concepts. Most participants reported that the instructions, item content, and response scales were clear and easy to understand and relevant. Conclusions: The content of the DLQI included all important and relevant concepts from the perspective of patients with moderate to severe plaque psoriasis. This study provides further support for the content validity of the DLQI in this population.