 The study investigates the completeness of survey data, audio recordings, and passively collected location data from three smartphone-based studies of people with a myotrophic lateral sclerosis. Despite patients' progressive physical and cognitive decline, time to discontinuation was higher than in typical smartphone studies. The study provides an important benchmark for participant engagement in a neurodegenerative population and suggests that collecting passive data and identifying participants who are likely to adhere during the initial phase of a study can increase data completeness. This article was authored by Anna L. Buchanhorst, Catherine M. Burke, Zoe Scheyer, and others.