The construct validity of real-world digital mobility outcomes in people with chronic obstructive pulmonary disease

Background: The clinical validity of digital mobility outcomes (DMOs) in chronic obstructive pulmonary disease (COPD) has yet to be established.

Aim: To evaluate the construct validity of 24 DMOs measuring walking activity (number of steps, number of walking bouts (WB), WB duration) and gait (walking speed, cadence, stride length) in people with COPD by assessing convergent, divergent, and known-groups validity.

Methods: 551 people with COPD were recruited from 7 European sites and monitored for 7-days in a real-world setting using a single wearable device. Functional capacity (6-minute walk distance (6MWD)), health status (COPD assessment test), dyspnoea (modified medical research council (mMRC) dyspnoea scale), lung function (forced expiratory volume in one second (FEV1%pred)), quadriceps muscle force, and physical activity difficulty (clinical visit-PROactive Physical Activity tool) were used as constructs for convergent validity testing. Diastolic blood pressure was used for divergent validity. Known groups validity was evaluated across GOLD I-IV, GOLD ABE stages, and mMRC groupings.

Results: Participants (37% females) had mean(SD) age of 68(8) years, FEV1%pred 54(20), and 6MWD of 403(116)m. Convergent validity was supported for 21 DMOs, with moderate to high coefficients (r=|0.4|-|0.65|) that matched those anticipated a priori. Comparable r values were observed across age groups, sex, recruitment sites, and exacerbation status. Similarly, 21 DMOs effectively distinguished between known groups. All DMOs supported divergent validity (r