The Use of Smartphone-Based Interventions to Improve Mental Health

Mental disorders are highly prevalent and cause a high burden of disease. Even though effective treatment approaches exist, there is a large treatment gap and a substantial proportion of non-responders to traditional face-to-face psychotherapy. New treatment approaches are required. The Grand Challenges in Global Mental Health initiative called for the development of mobile and IT technologies to increase access to evidence-based care. Internet-based psychotherapeutic interventions have been found efficacious. Smartphones are widespread, ensure high availability of their users, and are equipped with technologically rich sensors. In the context of electronic Health (eHealth) and mobile Health (mHealth), the potential of smartphone-based interventions has been recognized. Due to the relative novelty and interdisciplinarity of the field, several open research questions remain. This dissertation focuses on three selected research questions on how smartphone-based interventions can be used to improve mental health. The first publication provides evidence of the applicability of smartphone-based psychotherapeutic micro-interventions evoking mood changes in a real-world setting in a non-clinical sample (N = 27; n obs. = 335 micro-intervention sessions) across 13 days; data was collected in a larger randomized trial. Based on data from the same study, in the second publication, evidence is provided for the utility of a machine learning-based random forest (RF) algorithm for the prediction of smartphone-based psychotherapeutic micro-intervention success regarding mood amelioration, based on contextual information. In publication 3, based on data from healthy participants in a randomized controlled trial (N = 132), we explored whether efficacy expectancies could be successfully induced in a smartphone-based placebo mental health intervention lasting 20 days, in the context of digital placebo effects. These findings may pave the way for future endeavors to provide personalized digital mental health interventions and to further promote the promising field of eHealth and mHealth, in line with the precision medicine approach.