The construct validity of real-world digital mobility outcomes in people with COPD

Background Recent advances in wearable technologies make it possible to accurately quantify real-world mobility performance through technically validated digital mobility outcomes (DMOs). The aim of the present study was to evaluate the construct validity (convergent, divergent, and known-groups validity) of 24 DMOs quantifying walking activity (amount and pattern) and gait ( pace, rhythm and bout-to-bout variability) in people with COPD. Methods Part of the Mobilise-D observational cohort study, people with COPD, recruited from seven European sites, wore an activity monitor for 7 days during daily life. Functional capacity, health status, dyspnoea, lung function, quadriceps torque and experience of difficulty with physical activity were used as constructs for convergent validity testing (Pearson/Spearman correlation coefficients). Diastolic blood pressure was used as an unrelated construct for divergent validity (criterion: |r|<0.2). Known-groups validity was evaluated across Global Initiative for Chronic Obstructive Lung Disease (GOLD) stages (I–IV), GOLD ABE and modified Medical Research Council dyspnoea grades (linear models with p-for-trend). Results 549 participants (37% females), had mean±SD age of 68±8 years, post-bronchodilator forced expiratory volume in 1 s (FEV1) 54±20% predicted and 6-min walk distance 416±119 m. Convergent validity was supported for the majority of DMOs (17 out of 24) with correlation coefficients meeting or exceeding the a priori hypotheses by clinical experts. All DMOs supported divergent validity. 22 out of 24 DMOs distinguished between disease severity groups successfully. Expert consensus supported construct validity of 17 DMOs. Conclusions Construct validity was supported for all walking activity (amount and pattern) DMOs, and most of the gait ( pace, rhythm, and bout-to-bout variability) DMOs, indicating the clinical utility of these measures.