Fig. 2

Linear regression plot in the training set (a) and the test set (b). Regression equations (bold solid line) are \(y=1.102x-0.388\), R² = 0.649, p < 0.0001 (a), and \(y=1.073x-0.335\), R² = 0.700, p < 0.0001 (b). The 95% confidence and prediction intervals are also reported (dashed and solid lines, respectively)