A qualitative investigation of the relevance of skin irritation and self-confidence bolt-ons and their conceptual overlap with the EQ-5D in patients with psoriasis

Objectives A number of bolt-ons have been proposed for the EQ-5D, including two psoriasis-specifc bolt-ons, skin irritation and self-confdence. The study investigates and compares the relevance and comprehensiveness of these psoriasis-specifc bolt-ons and the EQ-5D-5L and explores the potential conceptual overlaps between the existing fve dimensions and the two bolt-ons. Methods Psoriasis patients were purposively sampled according to age and gender. Semi-structured interviews, where participants were asked to complete the EQ-5D-5L and the bolt-ons while thinking aloud, were conducted. Probes were used to investigate the thought processes of patients regarding the dimensions, wording, recall period and relevant concepts not captured by the EQ-5D-5L and bolt-ons. Data were analysed thematically. A focus group was used to confrm the fndings. Results Overall, 16 patients completed the interviews. Sixteen and ffteen patients considered skin irritation and selfconfdence relevant areas to describe psoriasis problems. Three patients considered itching a form of discomfort, and thus, pointed out a potential overlap between pain/discomfort and skin irritation. Twelve patients reported overall 10 general health- or psoriasis-related concepts that are not captured by the EQ-5D-5L, including itching, social relationships and sex life. Eleven patients reported that the recall period of the EQ-5D-5L might be subject to bias because of the daily or withinday fuctuations of their symptoms. Conclusions The skin irritation and self-confdence bolt-ons contribute to improve content validity of the EQ-5D-5L in patients with psoriasis. The qualitative approach taken in this study expands the existing methodological framework for the development and testing validity of bolt-ons for the EQ-5D.