Practice Effects in Mobile Tests of Cognition, Dexterity & Mobility in Multiple Sclerosis Patients: Data Analysis of a Smartphone–Based Observational Study (Preprint)

BACKGROUND Smartphones and their inbuilt sensors allow for the collection of a wealth of data about their owners. While passively collected data such as step counts can already provide meaningful insights, active tests allow for measuring function in more specific tasks. This could improve disease characterization and monitoring and could potentially support treatment decisions in multiple sclerosis (MS), a multifaceted chronic neurological disease with highly variable clinical manifestations. One challenge that has to be overcome in the assessment of changes over time is the analysis and interpretation of practice effects. OBJECTIVE In this study, we aimed to identify practice effects in active tests for cognition, dexterity, and mobility in user–scheduled, high–frequency, smartphone–based testing. METHODS We analyzed data from 251 self–declared persons with MS with a minimum of 5 weeks of follow–up and at least 5 tests per domain in the Floodlight Open study, a self–enrolment study accessible by smartphone owners from 16 countries. The collected data are openly available for scientists. Using bounded growth mixed models and quantile regression, we characterized practice effects for three different tests: Symbol Digit Modalities Test (SDMT) for cognition, Finger Pinching for dexterity, and Two Minute Walk for mobility. RESULTS Strong practice effects were found for N=4388 SDMT and N=17945 Finger Pinching tests with modelled boundary improvements of 39.6% (38.6%–40.9%) and 85.9% (83.2%–88.9%) over baseline, respectively. Half of the practice effect was reached after 9 repetitions for SDMT and 27 repetitions for Finger Pinching, 90% were reached after 31 and 89 repetitions, respectively. While baseline performance levels were highly variable across participants, no significant differences between the practice effects in low–performers (5th and 25th percentile), median performers and high performers (75th and 95th percentile) were found for SDMT (β = 1.0–1.2 additional correct responses per repetition in the linear phase). Only small differences were observed for Finger Pinching (β = 0.3–0.7 additional successful pinches per repetition in the linear phase). For N=12997 Two Minute Walk tests, no practice effects were observed at all. CONCLUSIONS Smartphone–based tests promise to help monitor disease trajectories of MS and other chronic neurological diseases. Our findings suggest that strong practice effects in cognitive and dexterity functions have to be accounted for in order to identify disease–related changes in these domains, especially in the context of personalized health and in studies with no comparator arm. In contrast, changes in mobility may be more easily interpreted due to the absence of practice effects.