Background Analysis of clinical trials with missing data requires statistical assumptions. When novel digital outcome measures are used, it is particularly important to understand trial participants’ experiences with the device. This can help illuminate the reasons for and specific patterns of missing data, thereby informing plausible missing data assumptions.Methods A patient and public involvement and engagement (PPIE) activity bridged statistical concepts on missing data with lived experiences of individuals who had participated in studies with digital outcome measures. Ten PPIE contributors attended three meetings, which were aimed to (i) introduce key statistical concepts and set the scene, (ii) discuss experiences of using digital devices in research studies, and (iii) consolidate learning and reflect on implications. In addition, contributors provided input via pre- and post-meeting surveys.Results Reasons for missing data in digital outcome measures were highly context dependent and varied according to the device, study population and environmental/cultural context. Identified reasons included operational aspects of the device, unresolved technology issues, and practicalities in daily life such as weather or season affecting comfort and the need to remove devices for religious, exercise or hygiene activities. Previous experience of using digital devices and receiving feedback from devices influenced levels of engagement. Although contributors did not report disengaging with devices in ways directly related to the outcome being measured, informative missingness was considered as important.Conclusions The PPIE activity was a feasible and valuable approach to exploring patient and public perspectives on the reasons for and patterns of missing data in digital outcome measures. Lived experience may shed light on reasons for missing data that may be overlooked by researchers; for example, religious activities affecting device removal was a key learning point. Incorporating PPIE discussions within ongoing trials may help inform statistical analyses and improve trial conduct. For future PPIE activities, purposeful recruitment and providing different modes of engagement, such as anonymous surveys, are recommended.