Here is the design of a clinical trial:

Official Title: Clinical Features, Management and Outcomes of Severe Ischaemic Stroke in Tertiary Hospitals in China: a Multi-centre Prospective Observational Study

Included conditions:
- Severe Ischaemic Stroke
- Malignant Ischaemic Stroke

Study Armgroups:
- {'label': 'Severe ischaemic stroke', 'description': 'patients with severe stroke on admission', 'interventionNames': ['Other: routine medical care']}
- {'label': 'Malignant ischaemic stroke', 'description': 'patients without severe stroke on admission but developing it in hospital', 'interventionNames': ['Other: routine medical care']}
- {'label': 'Mild to moderate ischaemic stroke', 'description': 'patients without severe stroke from onset to discharge', 'interventionNames': ['Other: routine medical care']}

Interventions:
- {'type': 'OTHER', 'name': 'routine medical care', 'description': "This is an observational study for clinical course and outcomes of severe ischaemic stroke; therefore, interventions are prescribed by responsible doctors based on patients' clinical conditions, which is not interfered by current study", 'armGroupLabels': ['Malignant ischaemic stroke', 'Mild to moderate ischaemic stroke', 'Severe ischaemic stroke']}

Primary Outcomes:
- {'measure': 'Functional outcome at 3 months after stroke onset', 'description': 'Modified Rankin scale score of patients at 3 months after the onset of ischaemic stroke.', 'timeFrame': '3 months after stroke onset'}

Please estimate the sample size based on the assumption: 
At least 10 events per variable, testing 5-10 variables, and a withdrawal rate of 10%
Sample size estimation
          This is an observational study with a primary aim to describe the clinical features and outcomes of patients with severe ischaemic stroke, which would often not require sample size estimation. Therefore, we calculate the sample size for the logistic analysis for predicting malignant brain oedema, for which we anticipate to test 5â10 variables as potential predictors. Based on the criteria of at least 10 events per variable,21 22 we will need 50â100 patients with malignant brain oedema. Assuming a proportion of 4% of general patients with ischaemic stroke would develop malignant brain oedema,1 a sample of 1250â2500 patients is required. In this observational study, we aim to recruit 2500 patients in order to allow a possible withdrawal rate of 10% and provide sufficient information on different subgroups of patients for further analyses.