Here is the design of a clinical trial:

Official Title: Celecoxib Versus Placebo as an Adjunct to Treatment-as-usual in Children and Youth With Obsessive-compulsive Disorder: A Single-site Randomized Quadruple-blind Phase II Study

Included conditions:
- Obsessive-Compulsive Disorder
- Pediatric Psychiatric Disorder

Study Armgroups:
- {'label': 'Celecoxib', 'type': 'EXPERIMENTAL', 'description': 'Celecoxib 50 mg orally twice daily (if weight 10-25 kg) or 100 mg orally twice daily (if weight \\> 25 kg) for 12 weeks. Used as adjunct to treatment-as-usual.', 'interventionNames': ['Drug: Celecoxib']}
- {'label': 'Placebo (microcrystalline cellulose)', 'type': 'PLACEBO_COMPARATOR', 'description': 'Placebo capsules identical to celecoxib. One capsule orally twice daily for 12 weeks. Used as adjunct to treatment-as-usual.', 'interventionNames': ['Other: Placebo']}

Interventions:
- {'type': 'DRUG', 'name': 'Celecoxib', 'description': 'Selective COX-2 inhibitor; nonsteroidal anti-inflammatory drug (NSAID)', 'armGroupLabels': ['Celecoxib'], 'otherNames': ['MINT-CELECOXIB', 'NDC Code: 0025-1525', 'ATC Code: M01AH01', 'Canadian DIN: 02412497']}
- {'type': 'OTHER', 'name': 'Placebo', 'description': 'Microcrystalline cellulose', 'armGroupLabels': ['Placebo (microcrystalline cellulose)']}

Primary Outcomes:
- {'measure': "Children's Yale-Brown Obsessive-Compulsive Scale, 1st Edition (CY-BOCS-I)", 'description': 'The CY-BOCS is a well-validated clinician-rated measure to assess obsessive-compulsive symptom severity. This results in two subscale total scores, Obsessions and Compulsions, each ranging from 0-20, with a higher score indicating greater symptom severity. These subscale scores are summed to provide a total score, ranging from 0 to 40, that is used to measure overall OCD symptom severity.', 'timeFrame': '12 weeks (adjusted for baseline severity)'}

Please estimate the sample size based on the assumption: 
A correlation of 0.5 between baseline and final CY-BOCS score, 80% power, directional one-tailed alpha, and imputation for missing follow-up data due to attrition.
Sample size calculation
        The sample size of 80 participants (40 per arm) was estimated on the basis of the primary hypothesis. If we assume a power to detect a minimally clinically significant between-group difference in CY-BOCS scores of 2.5 with an SD of 5 (equivalent to a Cohenâs d effect size of 0.5 and roughly based on two existing studies of adjunctive celecoxib in adults23 24) a correlation of 0.5 between baseline and final CY-BOCS score, and a sample size of 40 participants per arm, we will have power of 80% to detect a between-group difference using a directional, one-tailed alpha (celecoxib<placebo) using analysis of covariance. Missing follow-up data due to attrition will be imputed (as described in detail in the Statistical Analysis section below). Our recruitment target is similar to pilot studies of adjunctive celecoxib in other psychiatric disorders.19