Overview of the assessments
| Activity/assessment | T-1 | T0 | T1 | T2 | T3 |
| Prestudy | Baseline (week 0) | 4 weeks after T0 | 12 weeks after T0 | 6 months after T0 | |
| Eligibility screen | X | ||||
| Informed consent | X | ||||
| Primary outcome | |||||
| Insomnia severity (ISI) | X | X | X | X* | |
| Secondary outcomes | |||||
| Sleep quality (PSQI) | X | X | X | X | |
| Quality of life (AQoL-8D) | X | X | X | X | |
| Depressive symptoms (QIDS-SR16) | X | X | X | X | |
| Anxiety symptoms (GAD-7) | X | X | X | X | |
| Somatic symptoms (SSS-8) | X | X | X | X | |
| Costs (TiC-P) | X | X | X | ||
| Potential treatment moderators and mediators | |||||
| DBAS-10 | X | X | X | X | |
| Pre-sleep arousal (PSAS) | X | X | X | X | |
| Fatigue (BFI) | X | X | X | X | |
| Stress (PSS) | X | X | X | X | |
| Sleep hygiene behaviour (SHI) | X | X | X | X | |
| Emotion regulation (CERQ-short) | X | X | X | X | |
| Intervention-related variables | |||||
| Alliance (WAI-I) | X† | ||||
| Technological alliance (TAI-OT) | X† | ||||
| Client satisfaction (CSQ-8) | X | ||||
| Adverse events and negative effects (NEQ, Questionnaire on adverse effects of CBT-I) | X | X | |||
| Dropout Questionnaire | X‡ | ||||
*The ISI at T3 (6 months after T0) is the primary outcome of this trial.
†Only in patients of the intervention groups (IG1, IG2, IG3) who entered step 2 of the stepped care model.
‡Only in patients of the intervention groups (IG1, IG2, IG3) not completing at least 80% of the internet-delivered intervention.
AQoL-8D, Assessment of Quality of Life instrument; BFI, Brief Fatigue Inventory; CERQ-short, Cognitive Emotion Regulation Questionnaire; CSQ-8, Client Satisfaction Questionnaire; DBAS-10, Dysfunctional Beliefs and Attitudes about Sleep Scale; GAD-7, General Anxiety Disorder 7 questionnaire; ISI, Insomnia Severity Index; NEQ, Negative Effects Questionnaire; PSAS, Pre-Sleep Arousal Scale; PSQI, Pittsburgh Sleep Quality Index; PSS, Perceived Stress Scale; QIDS-SR16, 16-item Quick Inventory of Depressive Symptoms in the self-report format; SHI, Sleep Hygiene Index; SSS-8, Somatic Symptom Scale 8; TAI-OT, Technological Alliance Inventory; TiC-P, Trimbos/iMTA questionnaire for costs associated with psychiatric illness; WAI-I, Working Alliance Inventory for guided Internet interventions.