Hi, I am just a little confused of mian effect in the analysis of variance (ANOVA) when you include or do not include an interaction term. Let's assume a simple case of 2-way ANOVA with 2 factors A and B, each with 2 levels. If it shows that main effect for A is significant when the interaction between A and B is NOT included, and the main effect for A is NOT significant when the interaction is included, what simply does this difference mean? I understand that main effect for A generally means averaging over levels of B, is this explanation for the situation when interaction is included or is not included or is irrelavant?
And if my interest is in the main effect of A, in the above senario, should I include the interaction (thus lose the significance) or not include the interaction (thus keep my significance)? Thanks! ______________________________________________ [email protected] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
