Comparison of the predictive power for survival analysis of gene-level, GSVA, PLAGE, single sample GSEA (ssGSEA) and combined z-score (zscore) on simulated data. Each panel corresponds to a different sample size of the simulated data. The y-axis shows the concordance index values of predicting survival risk on test data from 100 independent simulations. On top of each boxplot the p-value of the t-test for no difference in means between GSVA and the corresponding method is reported. The method gene refers to a simple gene-level survival model built from the top 10 genes with lowest p-values reported by the Wald test performed on the training data. Diamonds indicate mean values in boxplots.