Hint1: There are two ways to do this in R. You can manually create dummy variable columns; or use the factor(region) in the lm function: lm(Y~infection+factor(Region)+infection*factor(Region)). Although the factor() method can generate the summary for the full model quicky, it is not as flexible as the dummy variable method to evaluate the parameters in the model. Hint2: You may use the relevel() function in R to change the baseline category. For example, if you want to use the second, or the NE category as the baseline, do data$region<-relevel(data$region,2). This is useful when you are not comparing the mean response value of Y in a level to that in the baseline level