Exploring the content validity of the EQ-5D-5L and four bolt-ons (skin irritation, self-confidence, sleep, social relationships) in atopic dermatitis and chronic urticaria.

Background: The objective of this study was to assess the content validity of the EQ-5D-5L and four bolt-ons: skin irritation, self-confidence, social relationships and sleep, for people with atopic dermatitis (AD) and chronic urticaria (CU).

Methods: Adults with AD or CU in the United Kingdom, with varying levels of severity, participated in either online or in-person semi-structured interviews. During the interviews, participants were first asked about the symptoms and impacts of their condition. They were then asked to complete the EQ-5D-5L and four bolt-ons using 'think-aloud' and retrospective probing. Interviews were recorded, transcribed, then analysed using content and thematic analysis.

Results: Thirty participants (N = 15 with AD; N = 15 with CU) were interviewed. Participants spontaneously reported itch (AD: 100%; CU: 93%), self-confidence (AD: 100%, CU: 47%), sleep (AD: 53%; CU: 53%), and social relationships (AD: 27%; CU: 60%). The skin irritation bolt-on was the most important or relevant dimension for 60% of AD and 73% of CU participants. For all participants, skin irritation and self-confidence bolt-ons improved the EQ-5D-5L's comprehensiveness. Social relationships was more frequently ranked as the least relevant among the other bolt-ons.

Conclusions: This study assessed the content validity of four EQ-5D-5L bolt-ons within two patient populations. Skin irritation, self-confidence and sleep bolt-ons showed good evidence of content validity for people with AD and CU, providing support for their application in other skin conditions. The value of a social relationships bolt-on was less clear. Quantitative psychometric research is recommended to further support the use of bolt-ons in CU and AD.