The Construct Validity of Real-World Digital Mobility Outcomes in People with Chronic Obstructive Pulmonary Disease

Background Recent advances in wearable technologies make it possible to accurately quantify real-world mobility performance through technically validated digital mobility outcomes (DMOs). Aim 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 chronic obstructive pulmonary disease (COPD). Methods Part of the Mobilise-D observational cohort study, people with COPD, recruited from seven European sites, wore an activity monitor for seven 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|