 The usual approach to calculating the sample size for a risk model is based on the rule of 10, that is the investigators require 10 times as many mortality events as there are predictors in the model. Our models will have 5 factors so the investigators require 50 events. Assuming a mortality rate of 20 suggests that the investigators require 250 patients in total. Note that this does not give us specific power to detect some predefined clinical effect this would be a very difficult calculation since pre- and post-NAC fitness are likely to be correlated but rather gives us enough data to fit risk prediction models to quantify the incremental benefit of post-NAC fitness. 