A self-control training app to increase self-control and reduce aggression-A full factorial design

Background: Research has shown that self-control training (SCT) is an effective intervention to increase selfcontrol and behaviour driven by self-control, such as reactive aggression. We developed an app that offers SCT by asking users to use their non-dominant hand for daily tasks, and aimed to examine whether participants that received SCT via app or e-mail, and received either one daily task or five tasks at once, improved more in self-control and decreased in aggression compared to each other and a control group. Methods: The design of this study was based on a pilot study in which a first version of the SCT app was developed and tested with students via a pretest-posttest design. Based on the outcomes of the pilot study, a 2 x 2 full factorial design (N = 204) with control group (n = 69) was used, with delivery via e-mail versus app and receiving one daily task versus five at once as factors. During four measuring points, self-control was assessed via the Brief Self-Control Scale (BSCS) and the Go/No-Go task, aggression was assessed using the Brief Aggression Questionnaire (BAQ). In the final questionnaire, open-ended questions were asked to gain insight into the app's points of improvement. Quantitative data were analysed using repeated measures linear mixed models, qualitative data were analysed via inductive coding. Results: While no interaction effects were found, analyses showed that only the BSCS-scores of participants that used the app significantly improved over time (F[3, 196.315] = 4.090, p = .008), no improvements were observed in the e-mail and control condition. No meaningful differences in aggression, the Go/No-Go task, and between the one- and five-task conditions and control groups were found. Qualitative data showed that while the opinions on SCT-tasks differed, participants were overall satisfied with the intervention, but wanted more reminders. Conclusions: The results of this study showed that an SCT app has the potential to bolster self-control. No convincing effects on aggression were found in this student sample, which might be explained by the relatively low levels of aggression in this target group. Consequently, the app should also be investigated in populations with aggression regulation problems. Future research might also focus on the use of SCT to improve other types of behaviour driven by self-control, such as physical activity or smoking. Finally, a more personalized version of the app, in which users can select the number and types of SCT-tasks, should be developed and evaluated.