Figure 2.

The nested cross‐validation strategy used in our study. (A) The flow chart of the nested CV strategy. The feature selection is implemented on the training set, rather than entire dataset. The performance is evaluated on independent test set in outer CV, which may avoid the overfitting problem. (B) The detailed explanation of the inner CV. In the inner CV, the training set is further divided into estimation set and validation set, the SVM parameters was estimated using a grid search method on the estimation set, the validation set is used to assess the optimal SVM parameters.