Here is the design of a clinical trial:

Official Title: Endoscopic Third Ventriculostomy for Adults With Hydrocephalus: Creating a Prognostic Model for Success - A Retrospective Multicenter Study

Included conditions:
- Hydrocephalus

Study Armgroups:

Interventions:

Primary Outcomes:
- {'measure': 'ETV success', 'description': 'The procedure is considered successful if the patient experience clinical improvement at first follow up and receives no further CSF diversion procedures, within one year of the initial procedure.', 'timeFrame': 'Evaluated 1 year after operation'}

Please estimate the sample size based on the assumption: 
The sample size calculation was performed using the 'pmsampsize' package in R. The goal is to achieve the necessary power to create a robust prognostic model.
Sample size
        Sample size was calculated using the âpmsampsizeâ package in R by Riley et al.29 The closest analogous predictive model is the ETVSS by Kulkarni et al7 and the estimation was created using prevalence and C-statistic from this model. This resulted in a minimum sample size of 429 patients, for a predictive model using 5 variables. There is no upper limit, as more patients would give a better foundation for the prediction model, especially in patients with aetiologies rarely treated with ETV such as iNPH or hydrocephalus caused by infection or SAH. Approximately 220 adult ETV patients have been identified in Copenhagen 2010â2017. Cooperation between several centres should easily provide the minimum required sample size and the necessary power to create a robust prognostic model. An estimate of at least 250 ETV procedures from each of the participating countries would result over 1000 patients.