The derivation and validation of ICISS will be conducted as two separate steps, described below. We will use R for all statistical analyses. We will assess predictive performance in terms of discrimination and calibration. Discrimination will be assessed by calculating the area under the receiver operating characteristics curve (AUROCC) and calibration will be assessed by comparing observed and predicted outcomes visually in a calibration plot and statistically by calculating the calibration slope. Confidence intervals for predictive performance measures will be estimated using a bootstrap approach.