Study aims and hypotheses
The present study aimed to expand the self-regulation technique of MCII to the context of sleep outcomes, namely sleep duration and sleep quality, in a non-clinical population. Our main objective was to compare the effects of sleep hygiene information only (SH) with the combined effects of MCII + SH regarding objective and subjective sleep parameters. We hypothesized that:(1) MCII + SH increase fitbit-measured sleep duration more than SH only,(2) MCII + SH increase self-reported (subjective) sleep duration more than SH only,(3) MCII + SH increase self-reported (subjective) sleep quality more than SH only.Moreover, we aimed to analyze associations of daily stress with sleep outcomes:(4) Self-reported daily stress is negatively associated with sleep outcomes (subjective sleep quality, fitbit-measured, and self-reported sleep duration). On the within-person level, this effect reflects shorter sleep duration and lower sleep quality on nights after days with higher than usual stress levels.As exploratory hypotheses, we expected stronger increases in the CAR in the MCII + SH group, as compared to the SH-only group, as well as a stronger decrease in self-reported stress in the MCII + SH group compared to the SH-only group.