Just-in-Time Coping Prompts for Reactive Digital Behavior in College Students

REACT is a five‐week micro‐randomized trial in University of Florida students age 18 andolder. Participants complete a baseline battery, wear a Garmin Venu 3, and respond tofive to six smartphone check‐ins per day. Week one is a no‐prompt run‐in that establisheseach participant's own baseline distribution of momentary affective variability, indexedby the mean square of successive differences on consecutive affect ratings. From week twothrough week five, the app evaluates up to six decision points per day. A decision pointis flagged when the participant's current variability exceeds their own 80th percentilethreshold, computed within person rather than against a group average. At each availabledecision point the app randomizes with probability 0.5 whether to deliver a brief copingmessage, and if so selects a message type from those eligible in that context.Availability rules exclude sleep, stale device data, a 60‐minute cooldown, a daily cap,and any safety override. Proximal outcomes are drawn from the first check‐in within twohours after the decision point. Analysis uses weighted and centered least squares toestimate causal excursion effects, with pre‐specified moderators.