The coefficient of multiple determination (R2) for a fitted plane and the modeled response surface with a statistical test of differences between these two ways of representing the data.

The R2 is a measure of the goodness of fit and was calculated from the total and residual sum of squares (SS) according to Eq 3. The fitted plane represents a plane tilted to best fit the data (by polynomial regression), whereas the modeled response surface is presented in Figs 1, 2 and 5. The p-values are from Fishers-F test of variance comparing the residuals from the fitted plane with the modeled response surface.The coefficient of multiple determination (R2) for a fitted plane and the modeled response surface with a statistical test of differences between these two ways of representing the data.