Selection of features for the model. Leave-one-out cross validation (LOOCV) is performed on all possible gene signatures, ranging from 50–250 features. Then, the performance characteristics of this bootstrap test are used to select an optimal number of genes (features) with which to build the signature. (A) Maximum area under the curve is achieved with signatures containing 105, 107, 108, 109 and 111 features. (B) The sum of deviance of the predicted probabilities is minimized by selecting the signature that contains 108 features.