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

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).

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.

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.

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.