Fig. 1. Systematic comparison of classification and regression performance of SML and DL methods.

Performance for several SML and DL methods for multiple classification and regression tasks was assessed using UK Biobank structural MRI data of 12,314 subjects (tasks A, B, and C) and ADNI structural MRI data of 828 subjects (task D). A rigorous cross-validation procedure was conducted via 20 random partitions of the data into training, validation, and test sets. For each repeat, the hyperparameters were tuned on the validation data and reported performance was evaluated on the held-out test set. The SML models were trained/tested on gray matter features reduced by three different feature reduction methods. In contrast, the DL models were trained on the unreduced (i.e., 3D voxel space) preprocessed gray matter maps.