Sampling time error in EuroSCORE II

Seasonal variation in mortality after cardiac surgery exists. EuroSCORE II accrued data over a 12-week period from May to July 2010. We investigated whether the accrual period for EuroSCORE II had a different mortality rate compared with the rest of the year. We found in a study population of 18 706 that the accrual period of EuroSCORE II may introduce bias into the predicted mortality, potentially reducing the accuracy of the new model.