I am trying to fit a model with 4 parameteres on one response. I have 32 points and the model contains linear, quadratic and interaction terms. Now when i apply the Step AIC method most of my square terms drop out (which i think is not correct if physics is concerned) So is there any way to force square terms whicle applying AIC. Also in what way aov() differs anova(lm). Is there any other way to select the regressin model terms? Thanks in advance. Vinod ____________________________________________________________________________________ Sucker-punch spam with award-winning protection.