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|