Randomization and masking
Participants were randomly assigned to either a dCBT-I intervention or a waitlist control group using a 1:1 randomization sequence with no stratification factors. The randomization sequence was kept by recruiting members of the study team who were unaware of previous allocations and assigned participants strictly in the temporal order of baseline completion, on which the study team had no influence (participants decided when to complete the baseline assessment online). Due to the nature of a behavioral intervention, participants were not blinded to the intervention and were aware of their group allocation. All-participants were informed that the study was setup to test the effectiveness of the digital intervention. Data was blinded before analysis to mask group allocation.