Study design and procedure
BLIND
This study used a two-arm randomized controlled trial design with a pretest (baseline), weekly assessments at the end of every week (weeks 1–7), a posttest (week 8), and a follow-up assessment (week 12). Participants were randomly assigned to one of the two conditions: the treatment group or the comparison group. The allocation was computer generated when participants declared interest for study participation and block randomization was used to ensure that the two groups are comparable in terms of sample size. Participants were blind to which condition they were in. The CONSORT flow diagram of the study is shown in On the first study day, all participants were asked to complete an online pretest on Qualtrics and to wear their Fitbit Charge 4 every day for at least 8 weeks from when they wake up to when they go to bed. During the first study week, participants were only asked to wear the Fitbit to establish their baseline activity. Across the study, participants also completed weekly assessments of self-control. After 8 weeks (1 baseline week and 7 study weeks), participants were asked to complete an online posttest and after 12 weeks an online follow-up assessment.