Usage of an App-Based Addiction Prevention Program for German Vocational Students: Secondary Analysis of Data From a Cluster Randomized Controlled Trial.

Background: Digital interventions have been successfully used to address addictive behaviors in adolescents and young adults. However, maintaining consistent usage remains a challenge. There is limited evidence on the determinants of usage with multiple behavioral interventions among vocational students. Objective: This paper aims to describe how vocational school students used the app-based addiction prevention program "ready4life" and to analyze student characteristics as potential determinants of intervention usage. Methods: A 2-arm cluster randomized trial evaluated "ready4life" among German vocational students aged ≥16 years. After downloading the app during class, students completed an anonymous screening and received individual risks and competencies feedback. Intervention participants (n=1286) received 4 months of individual app-based coaching, with weekly chat contacts with a conversational agent. They were asked to choose 2 of 6 modules: alcohol, tobacco, cannabis, social media and gaming, stress, and social competencies that were delivered sequentially in a random order. In addition to the weekly chats, users could self-initiate chat dialogues at any time. Chats included media (videos, images, or links), quizzes, and contests. Control participants (n=1282) received a link to health behavior information and could access coaching after 12 months. Results: Usage was low among intervention participants who received their assigned intervention (n=1266; females n=569, 44.9%; mean age 19.53, SD 3.57 years). On average, participants started 4.8 (SD 5.1) and completed 4.3 (SD 5.2) of 16 weekly in-app chats. Most students (n=903, 71.3%) completed no self-initiated chats, and 50.2% (n=636) stopped using the app before week 3. Unadjusted negative binomial multilevel regression models showed that females completed significantly more weekly dialogues (P<.001; incidence rate ratio [IRR] 1.55, 95% CI 1.33-1.80), while fewer were completed by individuals with higher self-efficacy (P=.04; IRR 0.96, 95% CI 0.93-0.998), higher social competencies (P<.001; IRR 0.97, 95% CI 0.95-0.98), and individuals engaging in more addictive behaviors (P<.001; IRR 0.87, 95% CI 0.82-0.93). Concerning specific educational tracks, professionals, technicians, associate professionals, and vocational grammar school students had the highest number of completed weekly dialogues. Determinants of completed self-initiated chats and usage time largely aligned with the findings for weekly dialogues. Additionally, those with higher perceived stress completed significantly more self-initiated chats (P<.001; IRR 1.19, 95% CI 1.08-1.31). Age and year of education were not significantly associated with any of the usage parameters. Conclusions: Our study supports the existing evidence that maintaining consistent usage among adolescents and young adults is a major challenge for digital interventions. An important finding was that students with higher needs for support in terms of self-efficacy, social competence, and perceived stress showed higher intervention usage. In terms of health equity, additional efforts should be made to increase intervention usage among males, those with lower levels of education, and those with higher levels of addictive behaviors.