Previous research has shown the efficacy of (combinations of) individual components of cognitive behavioral therapy for insomnia (CBT-I), namely sleep hygiene education, sleep restriction, stimulus control therapy, deactivation/relaxation training, and cognitive therapy. However, their relative effects, i.e., their effects in direct comparison with each other, are yet to be assessed. By means of the Multiphase Optimization Strategy (MOST), this study aims to investigate the components' relative efficacy in order to identify the most effective component or combination of components for digitized treatment of chronic insomnia. A future study will verify this intervention's effect in a randomized controlled trial (RCT).

The DOSE Project employs the Multiphase Optimization Strategy (MOST) to evaluate the relative efficacy of the individual cognitive behavioural therapy for insomnia (CBT-I) components. The present study represents the optimization phase of MOST, which aims to identify which combination of CBT-I components produces the best expected outcome, while taking constraints, such as economy, scalability, treatment complexity, and usability, into account.

The main objectives of the DOSE Project are

1. To conduct MOST on a multi-component smartphone or web application targeting insomnia
2. To identify the components and combination of components that demonstrate the best expected obtainable outcome
3. To examine potential moderators of the effect of the individual treatment components on insomnia severity,
4. To determine which application build (i.e., combination of components) is optimal to test in a subsequent RCT.

This study employs a fractional factorial experimental design conducted with individuals experiencing moderate-to-severe insomnia. With random allocation, participants will receive a version of the application in which one or more of the five core CBT-I components (i.e., sleep hygiene education, sleep restriction, stimulus control therapy, deactivation/relaxation training, cognitive therapy) are presented in various combinations. The intervention lasts 10 weeks, including an initial one-week assessment period.

Baseline group differences (concerning socio-demographic, disease-related, and psychosocial data) will be explored to test the success of the randomization. If differences are found, sensitivity analyses will be made to evaluate their possible influence on the results. Main effects will be analysed using Mixed Linear Models (MLMs) based on the intent-to-treat sample, comparing aggregated groups of N = 2 x 320 (e.g., plus/minus sleep restriction or plus/minus sleep hygiene etc.) on all outcome variables. MLMs account for the hierarchical, non-independent nature of the data (i.e., repeated measures nested within patients and treatment conditions), testing the time*group interaction effect, reflecting the effect of treatment. Moderation analyses will evaluate whether individual differences in various baseline variables (e.g., physical function, expectations, computer proficiency, chronotype, etc.) influence intervention effects.

Inclusion Criteria:

• Adults (≥18 years)
• Individuals who report moderate-to-severe insomnia symptoms (a score ≥10 on the Insomnia Severity Index, ISI)
• Individuals with access to a smartphone or computer with internet connection
• Individuals who report sufficient technological proficiency (e.g., ability to download apps)

Exclusion Criteria:

• Children (<18 years)
• Individuals who report mild or no clinically relevant insomnia symptoms (a score <10 on the ISI)
• Individuals who have a shift-work schedule or are on maternity/paternity leave, if this impacts their sleep quality or amount of sleep
• Individuals who are unable to read Danish
• Individuals who report severe physical or psychological comorbidity with known effects on sleep (e.g., psychosis, cardiovascular disease, cancer, COPD)
• Individuals who report other diagnosed sleep or circadian rhythm disorders (e.g., sleep apnea, narcolepsy)
• Individuals who have previously used the "Hvil®"-app

All individual participant data collected during the study will be made available in an irreversibly anonymized form. However, only data of those participants can be shared who have explicitly given consent to this as part of their informed consent to study participation. This means that it may not be possible to share all data underlying a certain publication.

Data will be shared exclusively for research purposes.

No later than six months after publication, no end date.

Data will be shared exclusively with other researchers and for research purposes only. Researchers requesting the data will have to provide a methodologically sound research proposal clarifying how the data will be used and for what purpose.