I am new to running Ancova in R. I am trying to see if my categorical variable (time) is significant in my dependent variable (Sales) while holding all other variables in my model constant.
aov(Sales ~ Price+Merch+ACV+Items+Category+Time, data = PintsT)
My question is how are you confident the Pvalues are relevant when holding the other variables constant? Does it automatically assume this using a type 3 analysis?
Also when would you use * instead of + in between the independent variables?