Examining the effectiveness of financial vs. social incentives to participate in a smartphone ecological momentary assessment well-being study: protocol for a randomized controlled trial.

Ecological momentary assessment (EMA) enables the collection of real-time data on individuals' feelings, behaviors, and contexts through repeated short assessments, typically delivered via smartphones. Despite its value for understanding everyday determinants of well-being, EMA is less commonly implemented than traditional, retrospective self-report methods in many applied and community-based research settings, in part because of the participant burden it can impose. This study protocol describes a randomized controlled trial designed first to estimate invitation-stage willingness to participate in an explicitly described smartphone-based EMA study recruited through a public community platform, and second to evaluate whether scalable financial and social incentives increase this willingness in this setting. Specifically, the study investigates how a lottery-based financial incentive and a non-financial social incentive influence willingness to participate (Yes/No) in an explicitly described EMA study focused on the impact of urban environments on subjective well-being. It also examines reasons for non-participation among those unwilling to participate, as well as alternative incentive preferences that could motivate future participation. The study targets 4,809 users of a digital community platform for residents, workers, and visitors in King's Cross, London. Using a stratified block randomization procedure with randomly permuted block sizes, participants are allocated to one of three conditions: a financial incentive (prize draw for shopping vouchers), a social incentive (invitation to a study feedback event), or a control condition (no incentive). Randomization is stratified by residential status. Invitations describing the EMA study in the neighborhood are sent to user email addresses and willingness-to-participate responses are collected through a brief follow-up questionnaire. Logistic regression will test differences across groups, while secondary analyses will explore subgroup variations by age, gender, and residential categories, as well as reported reasons for non-participation and preferred incentive alternatives. This trial is expected to provide evidence on invitation-stage willingness to participate and on the effectiveness of scalable financial and social incentives for promoting participation in EMA-based well-being research. Together with insights into reasons for non-participation and preferred incentive alternatives, these findings will inform scalable approaches to public engagement with smartphone-based EMA in health and well-being studies.