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).

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|<0.2). Known-groups validity was evaluated across GOLD stages (I-IV), GOLD ABE, and mMRC dyspnoea grades (linear models with p-for-trend).

Results
549 participants (37% females), had mean(sd) age of 68(8) years, post-bronchodilator FEV1 54(20) %pred and 6-minute 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. Twenty-two out of 24 DMOs successfully distinguished between disease severity groups. 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.