I have a MINITAB printout I was hoping someone could help me with. My question is- from the table below how do i distinguish between a main effect and an interaction?

Q. Three drug treatments are compared at three sites. The treatments consist of two dosages (low and high dose) of an experimental drug and a control drug. The results were analysed by two-way ANOVA with interaction. The ANOVA is shown below.

Analysis of Variance for response

Source DF SS MS F P
site 2 21.301 10.651 0.47 0.656
dose 2 185.404 92.702 4.09 0.108
site*dose 4 90.654 22.663 7.05 0.000
Error 63 202.574 3.215
Total 71 499.933


Thanks, Ariele