Here is the design of a clinical trial:

Official Title: A Randomised Multicentre Controlled Trial of Gastrectomy With or Without Prophylactic Abdominal Drainage. The Abdominal Drain in Gastrectomy Trial (ADiGe Trial)

Included conditions:
- Gastric Cancer

Study Armgroups:
- {'label': 'Drain', 'type': 'SHAM_COMPARATOR', 'description': 'Participants enrolled in this arm have an abdominal drain positioned at the end of the operation (any type, inserted from right flank with the tip close to the esophago-jejunal or Gastro-jejunal anastomosis and the duodenal stump). Drain will stay in place until postoperative day (POD) 4th (drain output and quality will be registered). If normal drain debt and patient have no abdominal complications that need reoperation and/or percutaneous drain placement until POD 4, a methylene-blue test is be performed (200 ml water + 5 ml blue orally, check drain after 60 minutes: negative test if no blu was seen in the drain). If negative-blue test drain can be removed according to centre preference (no strict POD defined); if positive-blue test complication will be treated according to centre preference. Only in this arm drain related complications are registered. Need for reoperation and/or percutaneous drain placement (primary outcome) are registered.', 'interventionNames': ['Device: Drain placement']}
- {'label': 'No Drain', 'type': 'EXPERIMENTAL', 'description': 'Participants enrolled in this arm do not have any abdominal drain placed at the end of the operation. Postoperative management (e.g. resume of oral intake, anastomosis integrity tests) is left to centre preference. Need for reoperation and/or percutaneous drain placement (primary outcome) are registered.', 'interventionNames': ['Device: Avoid drain placement']}

Interventions:
- {'type': 'DEVICE', 'name': 'Avoid drain placement', 'description': 'In No Drain arm (experimental) no abdominal drain is placed at the end of the operation.', 'armGroupLabels': ['No Drain']}
- {'type': 'DEVICE', 'name': 'Drain placement', 'description': 'In Drain arm (sham comparator) an abdominal drain is inserted in the abdomen from the right flank, passing below the liver (close to the duodenal stump) with the apex behind the esophago-jejunal (in total gastrectomy) or gastro-jejunal (in subtotal gastrectomy) anastomosis.', 'armGroupLabels': ['Drain']}

Primary Outcomes:
- {'measure': '30 day reoperation AND/OR additional drain placement', 'description': 'Incidence of reoperation AND/OR percutaneous placement of an additional drain within postoperative day 30 (composite outcome)', 'timeFrame': '30 days after the operation'}

Please estimate the sample size based on the assumption: 
80% power, one-sided significance level of 5%, 10% dropout rate, one-sided Z test (unpooled).
Sample size
        According to a systematic review published in May 2020 [8], the cumulative incidence of reoperation in two RCTs was 7/115â=â6.1% (95% CI 2.5â12.1%) in the drain group and 3/115â=â2.6% (95% CI 0.5â7.4%) in the no drain group. Cumulative incidence of additional drain was 1/86â=â1.2% (95% CI 0.03â6.3%) in the drainage group and 2/84â=â2.4% (95% CI 0.3â8.3%) in the no drain group. Assuming a 70% of overlap between the two procedures in the drain group, the estimated proportion of the composite outcome is 6.44%, while assuming a 35% overlap in the no drain group, the estimated proportion of the composite outcome is 4.16%.
        Hence, we assumed a reference group proportion of 6.44%, and a treated group proportion of 10% under the null hypothesis of inferiority and 4.16% under the alternative hypothesis of non-inferiority. A sample size of 182 in each group, corresponding to 364 patients overall, achieves 80% power to detect a non-inferiority margin difference between the group proportions of 3.56% (=â10â6.44%), with a one-sided significance level of 5%. A power curve for treated group proportion ranging from 3 to 7% under the alternative hypothesis of non-inferiority is presented in Fig.Â 3.
Fig. 3Power curve as a function of treated group proportion ranging from 3 to 7% under the alternative hypothesis of non-inferiority. P0 (proportion in the control group)â=â6.4%; alphaâ=â0.05; n1â=ân2â=â182; P1.0 (proportion in the treated group under the null hypothesis of inferiority)â=â10%. The test statistic used is the one-sided Z test (unpooled)
        Considering a 10% dropout rate, 404 patients (202 in each group) are needed. In order to have a balanced percentage between total and subtotal gastrectomy, recruitment will end at 202 patients for each type of gastrectomy.