Strengths and limitations
sleep disturbance
This study has several strengths. First, intervention adherence and engagement were objectively captured via the study app. Second, participant retention was high, reducing the potential impact of missing data on study findings. Third, all study outcomes and analyses were prospectively registered, precluding any selective reporting of outcomes or nonpublication of findings. Fourth, participants were screened for poor sleep using a well-validated measure of sleep disturbance. Fifth, participants were given access to a restricted version of the One limitation of this study is that sleep quality and other mental health measures were captured immediately post-intervention with no follow-up period. Future research should aim to explore whether any outcome improvements are maintained over time, either with or without continued use of the interventions, as well as how frequently they need to be used to be beneficial. Such information could help to inform more meaningful per-protocol analyses in future RCTs, help to guide in-app engagement recommendations, and shed light on potential mechanisms of action. For example, if improvements in sleep following intervention use are short-lived, it might suggest that the audio tools predominantly act by counteracting presleep arousal or inhibitory cognitive processes, as opposed to changing underlying beliefs about sleep.Similarly, we were unable to conduct exploratory dose–response analyses in this study, and could not test whether increased use of the study interventions predicts larger improvements in sleep. This should be explored in a fully powered trial if we are to understand the true impact of the interventions. We also used a passive control group as opposed to an active control group in which participants engage with activities matched for duration, attention, and interest. Passive controls can lead to inflated estimates of treatment effects, and do not account for nonspecific placebo effects. Although it is useful in practical terms to estimate this combined effect of the Another limitation is that participants were predominantly White and approximately 70% female (though females have a higher risk of developing sleep problems than males [