We will use all available data from TITCO and create a temporal split sample, using the earlier data for derivation and the most recent data for validation. These two samples are henceforth referred to as the derivation sample and validation sample respectively. We will first estimate the required sample size of the validation sample to include the most recent 200 consecutive events, i.e. patients who died within 24 hours, and all non-events enrolled during the same time period.