Here is the design of a clinical trial:

Official Title: Internet-based vs Face-to-face Cognitive Behavioural Therapy for Obsessive-compulsive Disorder - a Randomized Controlled Non-inferiority Trial

Included conditions:
- Obsessive-compulsive Disorder

Study Armgroups:
- {'label': 'Face-to-face CBT', 'type': 'ACTIVE_COMPARATOR', 'description': '16 sessions of individual CBT delivered in 14 weeks.', 'interventionNames': ['Behavioral: Cognitive-behavioral therapy (face-to-face)']}
- {'label': 'Internet-based CBT', 'type': 'EXPERIMENTAL', 'description': 'Internet-based CBT (ICBT) with therapist support (14 weeks).', 'interventionNames': ['Behavioral: Internet-based Cognitive-behavioral therapy']}
- {'label': 'ICBT without therapist support', 'type': 'EXPERIMENTAL', 'description': 'Internet-based CBT without therapist support (14 weeks).', 'interventionNames': ['Behavioral: Internet-based Cognitive-behavioral therapy without therapist support']}

Interventions:
- {'type': 'BEHAVIORAL', 'name': 'Cognitive-behavioral therapy (face-to-face)', 'armGroupLabels': ['Face-to-face CBT'], 'otherNames': ['CBT']}
- {'type': 'BEHAVIORAL', 'name': 'Internet-based Cognitive-behavioral therapy', 'description': 'With therapist support', 'armGroupLabels': ['Internet-based CBT'], 'otherNames': ['ICBT']}
- {'type': 'BEHAVIORAL', 'name': 'Internet-based Cognitive-behavioral therapy without therapist support', 'armGroupLabels': ['ICBT without therapist support']}

Primary Outcomes:
- {'measure': 'Yale-Brown Obsessive-Compulsive Scale (Y-BOCS)', 'timeFrame': 'Change from baseline to treatmentweek 2, 4, 6, 8, 10 , 12, 15 and 3- and 12-month follow-up.'}

Please estimate the sample size based on the assumption: 
Variance of the random intercept: 10.5, variance for the random slope: 0.04, within-individual residual variance: 20.4, significance level not specified, power: over 90%, interim power analysis with 80 individuals.
Sample size calculation
        In order to provide accurate estimates for the power calculation in the current trial, weÂ used individual-level data from a previous study of therapist-guided ICBT with identical Y-BOCS assessments by blinded raters and six repeated observations.14 To calculate the required sample size, we used a bootstrap simulation with 1000 samples using the following assumptions, based on data from the previous trial: a variance of the random intercept of 10.5, a variance for the random slope of 0.04 and a within-individual residual variance of 20.4. With three treatment groups and eight observations (Y-BOCS) per patient, we estimated that a total of 120 participants would be needed to detect a slope difference between two groups (ie, group 1 vs group 2 and group 1 vs group 3) of 3 points at 3-month follow-up with over 90% power. We will request an interim power analysis by the KTA to test these assumptions, using data from 80 individuals, and adjust sample size if power is lower than anticipated (see onlineÂ supplementary file 1 for a detailed description).
        
          10.1136/bmjopen-2018-022254.supp1
          Supplementary file 1