Conclusions
health-promoting behaviors, SD
REGRESSION
This study is the first randomized trial demonstrating that incremental theories of health can increase because of a single-session smartphone-based intervention. Contrary to our assumptions, the intervention only led to an increase in performing health-promoting behaviors when delivered at a later point in time. Further studies are crucial to assure whether the observed time-dependent variation in effectiveness replicates. Incremental theories interventions might be most effective for individuals holding a stronger entity theory of health. Factors that favor the development of an entity theory of health should be investigated to identify population groups that would benefit most from the interventional approach introduced in this paper.This work was supported by an advanced postdoctoral grant from the University of Cologne awarded to SD. Open access funding was provided by the University of Vienna. The authors would like to thank Marina Hinssen, Anna-Lena Brans, Isabel Skuplik, and Leonie Wiegmann for their practical support. MS and SD were affiliated with the University of Cologne at the time of the trial. MS is now affiliated with the University of Vienna, and SD is now affiliated with the University of Bonn.Conflicts of Interest: None declared.Table S1. Regression coefficients and information criteria for comparing the multilevel models to predict health behavior engagement per day.CONSORT-eHEALTH checklist (V 1.6.1).