I am looking for contaminations on two different beaches N and S at two different times T1 and T2. Where it is suggested that Beach N has a higher risk of contamination than beach S and the levels vary according to the different times.
I have to create an experimental design to test if this is the case. At each time, we collect five samples on each beach and test each sample.
Taking the model that beach N has a greater risk of contamination than beach S.
I have to find the main effects of the factors and possible interactions between them.
And sketch the graph in which the model is supported at only one of the two sampling times.
So I got the explanatory variables, they are N and S (region) and T1 and T2 (Time). With the level of contamination as the response variable
but I am a bit confused as to how the main effects and the interactions can be found?
