Figure 1: The experiment workflow diagram and the data summary.

The harmonized, and joint-called PPMI and PDBP cohorts originate from the AMP-PD initiative. The PPMI cohort is split into K folds, where one fold is left as a holdout (internal) test set, and the emaining are used for model fitting. The training folds are split using an 80:20 ratio to form the training validation split. The training split is distributed among $\mathrm{N}$ clients using one of the split strategies to simulate the cross-silo collaborative training setting. FL Methods consist of a local learner and an aggregation method. Similarly, several central algorithms are used to fit the training data. The resultant Global FL models and the ML models resulting from central training are tested on the PPMI holdout fold (internal test) and the whole PDBP test set (external test).