Testing the construct validity of real-world digital mobility outcomes in multiple sclerosis

Background:

Wearable devices can measure real-world mobility and generate metrics known as digital mobility outcomes (DMOs). For people with multiple sclerosis (pwMS), these DMOs have not been clinically validated. This study aimed to evaluate the construct (convergent, divergent, and known groups) validity of a comprehensive panel of 24 DMOs in pwMS.

Methods:

PwMS were recruited to the Mobilise-D Clinical Validation Study, which involved 7-days of real-world mobility monitoring with a lower-back-worn wearable device. DMOs of walking amount, pattern, pace, rhythm, and variability domains were assessed. Convergent validity was evaluated against established clinical constructs (Expanded Disability Status Scale (EDSS), Timed 25-Foot Walk, Multiple sclerosis (MS) Walking Scale-12, and Patient-Determined Disease Steps) using a priori hypotheses. Divergent validity was tested against systolic blood pressure. Known-groups validity was assessed across three EDSS strata. An expert panel completed a standardised consensus process.

Results:

We included 556 participants: 65% women, mean (SD) age of 52.3 (10.7) years, and median (p25–p75) EDSS 5 (4–6). Convergent, divergent, and known-groups validity were supported for 19, 24, and 23 DMOs, respectively. Nineteen DMOs, covering all domains, reached consensus agreement.

Conclusion:

This study confirms the construct validity of 19 DMOs across all walking domains in pwMS, supporting their use in clinical research and practice. www.isrctn.com/ISRCTN12051706.