Developing and testing bolt-on enhanced EQ-5D-5L for assessing Chinese patients with chronic obstructive pulmonary disease: a mixed-methods study protocol

Introduction The EuroQol five dimensions questionnaire (EQ-5D) is widely used as a health-related quality of life (HRQoL) measure worldwide, but its sensitivity in detecting changes in health status among individuals with chronic obstructive pulmonary disease (COPD) remains suboptimal. Adding additional HRQoL dimensions (bolt-on items) to EQ-5D may enhance its sensitivity to specific diseases while preserving the original EQ-5D descriptive system. This study protocol documents the identification, development, selection and psychometric testing of respiratory-related bolt-on items for assessing COPD in China. Methods and analysis We will conduct a content review of the COPD disease-specific instruments to identify potential deficiencies in dimensions covered by the EQ-5D. Drawing from the dimensions identified in the content review, we will consult with clinical experts and conduct qualitative interviews with patients to identify and develop candidate bolt-on items that are relevant to COPD. Then, in the quantitative phase, we will assess the psychometric properties of the candidate bolt-on items among patients with COPD in China. Test–retest reliability will be examined using intraclass correlation coefficients for total scores and weighted kappa statistics for item-level agreement. Construct validity will be evaluated through convergent and divergent validity analyses using Spearman’s rank correlations. Known-groups validity will be tested by comparing five-level EQ-5D version (EQ-5D-5L) and EQ-5D-5L plus bolt-on scores across clinically defined subgroups using analysis of variance. The dimensional structure will be explored using exploratory factor analysis with maximum likelihood extraction and Promax rotation. Explanatory power will be assessed through ordinary least-squares regression with EQ visual analogue scale as the dependent variable, supported by Shorrocks–Shapley decomposition to quantify the contribution of each item to the explained variance. Discussion Based on the EQ-5D, Our study offers a new approach to measuring HRQoL in patients with COPD. Furthermore, it may offer valuable insights and serve as a reference for the development of bolt-on items for other diseases. Ethics and dissemination This study has received ethical approval from the Ethics Committee of the Centre for Health Management and Policy Research at Shandong University (no. ECSHCMSDU20240301).