Currently submitted to: JMIR mHealth and uHealth
Date Submitted: May 4, 2025
(closed for review but you can still tweet)
Warning: This is an author submission that is not peer-reviewed or edited. Preprints - unless they show as "accepted" - should not be relied on to guide clinical practice or health-related behavior and should not be reported in news media as established information.
A micro-randomized trial of planning interventions delivered via a Just-In-Time Adaptive Intervention for adult gamblers: Gambling Habit Hacker mobile app
ABSTRACT
Background:
People experiencing gambling problems often struggle to adhere to their intention to reduce time and money spent gambling. While many techniques exist to reduce gambling harm, consistently applying them across settings and at the right time remains challenging. Providing personalised, real-time support could enhance behaviour change efforts.
Objective:
This study evaluated a Just-In-Time Adaptive Intervention (JITAI) to help individuals adhere to gambling limits. Drawing on the Health Action Process Approach and Self-Determination Theory, the primary aim was to assess the effect of action and coping planning versus no intervention on adherence to expenditure limits. The primary proximal outcome was goal adherence, defined as unplanned expenditure (≥10% over planned expenditure per day). Secondary outcomes included intention strength, goal self-efficacy, and urge self-efficacy, all measured continuously.
Methods:
We conducted a fully automated and blinded micro-randomised trial (MRT) with 50:50 randomisation and a 6-month within-group follow-up. Participants were recruited online; eligibility included residing in Australia, enabling notifications, and seeking gambling support. The Gambling Habit Hacker smartphone app delivered tailored behaviour change techniques, including goal setting, action and coping planning, and self-monitoring. The MRT randomised 174 participants to test whether the app provided in-the-moment support for adhering to limits. Participants set personal expenditure goals and completed three Ecological Momentary Assessments (EMAs) daily for 28 days, tracking adherence, intention strength, self-efficacy, and high-risk situations. At each EMA, participants needing support were micro-randomised to receive action/coping planning with support or a control condition involving selection of a self-enactable strategy without support.
Results:
Of 238 enrolled participants, 174 completed at least one EMA. Most were male (68%) and reported moderate or mild gambling severity (52%). An intervention was delivered at least once to most participants (n = 140, 80%). Receiving an intervention did not increase the probability of adherence compared to no intervention. In contrast, supplementary analyses in which findings from the EMAs were collapsed across each day revealed the intervention was associated with lower rates of unplanned gambling expenditure when compared to the control condition. Within-group follow-up showed a large reduction in monthly expenditure (from $2,700 to just over $260) and gambling frequency (from 8–9 to 1–2 sessions) at six months. Significant improvements with small-to-large effect sizes were also observed at post-treatment and maintained at follow-up for gambling severity (dz = -0.91), self-efficacy (dz = -0.42), psychological distress (dz = -0.52), and well-being (dz = 0.70).
Conclusions:
Gambling Habit Hacker showed strong overall effects over time but no significant difference in adherence between intervention and control conditions. Given the strong effect over time, future studies should explore an optimised version of the app that is subject to a randomised controlled study design. Clinical Trial: This trial has been registered with the Australian New Zealand Clinical Trials Registry (ACTRN12622000497707) and was approved by the Deakin University Human Research Ethics Committee (2020-304).
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