Singularity problems with crossed categorical factors
I have 2 categorical factors. The first is type of covering material, with 2 types available. Since it is also possible to use no covering material, this factor has 3 levels. The second factor is the method to apply these materials and has 2 levels (without overlap or with overlap). I am interested in fitting a model with the main effects and the interaction. When I try it to run this way (Table s...