Hi, This is really more a stats question than a R one, but.... Does anyone have any familiarity with using the mean prediction squared error scaled by the variance of the response, as a 'scale free' criterion for evaluating different regression algorithms. E.g. Generate X_train, Y_train, X_test, Y_test from true f. X_test/Y_test are generated without noise, maybe? Use X_train, Y_train and the algorithm to make \hat{f} Look at var(Y_test - \hat{f}(X_test))/var(Y_test) (Some of these var maybe should be replaced with mean squared values instead.) It seems sort of reasonable to me. You get a number between zero and one out of it, with 1 the solution for constant fits. Anyone seen anything like this, or know anything about properties? Has it got a name? Zhou Fang