Psychometric testing of two respiratory bolt-on items to EQ-5D-5L in patients with obstructive airway diseases.

Objectives: Two recently developed respiratory bolt-ons were shown to improve the construct validity of EQ-5D-5L among community-treated patients with obstructive airway disease (OAD). We evaluated their psychometric properties, including responsiveness and reliability in a specialist-managed OAD cohort.

Methods: We performed in-depth interviews with ten OAD patients and ten clinicians to assess their content validity. We administered the Saint George's Respiratory Questionnaire (SGRQ), EQ-5D-5L and two respiratory bolt-on items, (physical impediment, R1 & symptoms, R2) in adult OAD patients at baseline and follow-up visits. We used the baseline data to compare among four EQ-5D versions, EQ-5D-5L, + R1, + R2 & + R1R2: (1) ceiling using individual item responses; and (2) Spearman's rho correlations (R) with SGRQ, (3) association with clinical characteristics using C-statistics from receiver operating characteristic (ROC) analyses, and (4) coefficient of determination from regression modelling using index/level sum scores. We used the follow-up data to compare intra-class correlation coefficients (ICCs)/Cohen's Kappas (κ) of "stable" patients; and standardized effect sizes/C-statistics of "better" patients using SGRQ and clinical criteria, across the four versions.

Results: Psychometric properties of the respiratory bolt-ons proved to be acceptable. We included 184 patients with a mean age of 54 (standard deviation, 18) years at baseline, and 120 at follow-up at 2.8 (standard deviation, 1.7) months. The ceilings were nullified in + R1, + R2 and + R1R2. Construct validity and responsiveness were consistently higher in + R2 and + R1R2 compared to EQ-5D-5L, while reliability remained comparable among the four versions.

Conclusions: Respiratory bolt-ons demonstrated good content validity and enhanced the psychometric properties of EQ-5D-5L in OAD.