 The sample size calculation for hypothesis 22A is not based on power but instead is based on the amount of data required to develop a robust and reliable risk model. The idea is to develop a risk prediction model based on preNAC factors and quantify its predictive ability e.g. using the ROC area. McCulloch BMJ, 2003 does something similar. Next the investigators will add postNAC fitness to the model and establish whether this extra data provides extra predictive ability. 