Predicted R-squared is a measure of how well the model predicts a response value. It is computed as
Pred.R2=1−[PRESSSSresidual+SSmodel]=1−[PRESSSStotal−SScurvature−SSblock]
The Adjusted R-squared and Predicted R-squared should be within approximately 0.20 of each other to be in “reasonable agreement.” If they are not, there may be a problem with either the data or the model.