Study Design and Procedures
BLIND
This study followed a longitudinal RCT experimental design with a 2-week follow-up. The trial started in January 2018 and ended in September 2018. Human resources managers were blind to the participants’ group allocation and participants were blind to the goals and hypotheses of the study; however, they were not blind to their group allocation. While blinding is of course desirable in practice, a naturalistic study is often not possible to achieve in a digital health intervention.Participants were randomly assigned to one of the two experimental conditions (intervention group or waitlist control group) after signing up and giving their informed consent. Randomization was implemented through a software program invoking an unbiased random number generator; subjects were assigned to a group without human intervention immediately after giving their consent. Measurements of all participants were collected online via Qualtrics at baseline (T0, week 0), midintervention (T1, week 2), postintervention (T2, week 4), and at the 2-week follow-up (T3, week 6). Participants belonging to the app (intervention) group were asked to first complete the questionnaires before downloading and starting to use the app. Reminders and invitations to the follow-up questionnaires were sent via email. Participants had 7 days to complete the questionnaires. As soon as they had completed the follow-up measurement, all participants were thanked and fully debriefed.The intervention lasted 4 weeks. During these 4 weeks, participants in the intervention group could complete a maximum of 28 sessions (1 per day) and track a maximum of 28 nights. However, it was completely up to the user to decide to what extent they wanted to engage with the app. They could also decide whether to use the app on their personal phone or their work phone. Reminders were sent through push notifications, although users had the option to turn them off. After the 4 weeks of the intervention, the interventional module within the app was withdrawn for the intervention group. A 2-week follow-up measurement was then taken to assess which gains from the 4-week intervention persisted. Participants belonging to the waitlist control group had no access to the intervention for the duration of the trial (ie, 6 weeks). They received access to the intervention and the tracking modules once the study was completed.