I ran the response surface modeling using central composite design. And I got this output. Can I take this model? The model is having lack of fit p value more than 0.05. But other parameters are not good. Such as the p values in x1 , x2 and x1:x2 are non-significant. The model gives the stationary points at pH=6.7 and Temp= 21.8. Are these stationary points are reliable given the structure of model. The output is attached herewith. I used the rsm package of R