Figure 1. Number of studies with more than 30% class imbalance and the percentage of studies that applied the class imbalance strategies, separated by PD prediction target. In the PD versus non-PD classification, PD versus non-PD versus other diseases classification, PD severity prediction, and PD symptoms quantification and progression prediction categories, 46% (27/59), 67% (16/24), 100% (30/30), and 40% (4/10) had class imbalance, but only 8% (5/59), 21% (8/30), 27% (8/30), and 10% (1/10) applied mitigation strategies, respectively. PD: Parkinson disease.