A Stepped Care Approach to Promoting Engagement in a Digital Health Intervention: Secondary Analysis of a Randomized Controlled Trial

BACKGROUND: Digital health interventions (DHIs) often struggle with participant engagement. A stepped care approach, starting with low-resource intensity strategies and escalating as needed, can optimize resource use. Yet its application and cost implications remain underexplored. OBJECTIVE: This study uses data from the iSIPsmarter experimental arm of a 2-group randomized controlled trial targeting sugar-sweetened beverage consumption in rural Appalachia. This study examines the demand and implementation costs associated with iSIPsmarter's stepped care engagement approach and simulates how variations in monitoring efficiency, demand, and stepped care intensity influence resource use and implementation costs to inform future implementation. METHODS: iSIPsmarter's stepped care process combined automated and human-supported components to enhance engagement across 6 web-based modules ("Cores") over 9 weeks. Participants who did not complete a Core received an automated email, followed by stepped care if still incomplete: a text (step 1, low-resource intensity) after 7 days and up to 3 telephone attempts (step 2, high-resource intensity) after another 7 days. Staff time was tracked to estimate implementation costs: monitoring averaged 3 minutes (US 1. 68), texts 2. 83 minutes (US 1. 58), and calls 5. 1 minutes (US 2. 85). Simulations explored 18 scenarios varying monitoring efficiency (20%, 50%, and 80% of trial-observed monitoring time and costs), stepped care demand (20%, 50%, and 80% of participants needing stepped care), and intervention intensity (low vs high). RESULTS: Among 126 participants, the mean stepped care contact was 1. 2 (SD 1. 3): 52 (41%) required none, 42 (33%) required 1 Core contact, 26 (21%) required 2, and 7 (6%) required 3. On average, participants completed 5. 2 (SD 1. 6) of 6 Cores. The mean stepped care implementation time per participant was 26. 46 (SD 11. 02) minutes, with a corresponding mean cost of US 14. 80 (SD 6. 16). Monitoring accounted for 78% of total cost (mean cost US 11. 61, SD 2. 37), with initial monitoring contributing 58% of total cost (mean cost US 8. 51, SD 2. 35). Simulations showed variation in time and cost based on monitoring efficiency. In low-demand, low-intensity scenarios, efficient monitoring required mean of 7. 47 (95% CI 7. 36-7. 57) minutes and mean cost of US 4. 18 (95% CI 4. 12-4. 24), while inefficient monitoring required a mean of 19. 58 (95% CI 19. 21-19. 95) minutes and mean cost of US 10. 95 (95% CI 10. 74-11. 16). In high-demand, high-intensity scenarios, efficient monitoring required a mean of 101. 80 (95% CI 101. 65-101. 96) minutes and mean cost of US 56. 92 (95% CI 56. 84-57. 01), while inefficient monitoring increased time to a mean of 146. 32 (95% CI 145. 92-146. 71) minutes and mean cost of US 81. 82 (95% CI 81. 60-82. 04). CONCLUSIONS: A stepped care approach can efficiently sustain engagement in DHIs by targeting support to higher-need participants. These findings offer actionable guidance for designing scalable, cost-effective interventions for real-world settings, as resource-efficient engagement strategies remain a persistent challenge for DHIs.