Study Design
health-promoting behaviors
We conducted a 2-arm, randomized trial to investigate whether fostering an incremental theory of health increases the frequency of performing health-promoting behaviors in daily life. The intervention was conceptualized as a delayed-start design [At the beginning of the study (day 0), all participants responded to an entry questionnaire to measure implicit theories of health, health locus of control, health-related self-efficacy, health-related outcome expectancy, health status, health value, health change motivation, and anthropometric (height and weight) and demographic variables (age, gender, education, and occupation). One day after responding to the entry questionnaire, the daily diary phase started. Over the course of 3 weeks (21 days), participants received daily invitations to complete a short questionnaire via texting distributed via SurveySignal [We chose the delayed-start design as it allows testing for intervention effects between and within both intervention arms [Overview of the intervention flow for the early and delayed intervention group. Links to view intervention materials were sent out at 8 AM on day 8 (early intervention group) or day 15 (delayed intervention group), and the links were valid for 12 hours.