Who stays and who plays? Participant retention and smartphone app usage in a longitudinal travel survey

Longitudinal studies have become increasingly popular for investigating changes in behaviour, but present additional challenges around participant recruitment, retention, engagement with survey tasks, additional burden and ultimately data quality. Personal technologies, particularly smartphones, have become integral to tackling these challenges but come with their own caveats around user acceptance and engagement. The current paper investigates these issues in the context of a longitudinal study of interventions designed to encourage use of public transport and increase associated physical activity in Tasmania, Australia. The study comprised multiple waves of data collection over a seven-month period in which travel data were collected using a smartphone app supplemented with user experience surveys. Attrition is lower for older participants, those engaging with the app more, and those responding to the research/environmental/health messaging of the survey as well as the potential for financial gain. App usage is lower among older participants while app engagement is stronger for males, those recording less travel and those indicating environmental reasons as a motivator for completing the study. Experiences with the app are mixed, participants report positive sentiments about the ease of use, hedonic motivation, and help in recalling travel; however, concerns are raised over the accuracy of trip recording, the associated burden of correcting trips, and reductions in smartphone battery-life. Despite the unplanned coincidence with the COVID-19 restrictions, outcomes provide important guidance around recruitment, retention and post-hoc analysis of results from longitudinal studies.