I have a couple of questions about contrasts but would also appreciate any suggestions for relevant literature.
I am carrying out a GLM (binomial). There are 3 Factors (A,B,C) - A has 3 levels, B & C have 2. As main effects all factors are significant, and for factor A I can test the significance between the levels with orthogonal contrasts (-1, 0.5, 0.5)(0, -1, 1).
There is also a significant interaction between A & B and this is where I am getting stuck/confused.The interaction between A & B produces 6 treatments (A1*B1, A1*B2, A2*B1, A2*B2, A3*B1, A3*B2) Do I need to construct a matrix with 6 levels? For example...
(-1, 0.2, 0.2, 0.2, 0.2, 0.2) ( 0, -1, 0.25, 0.25, 0.25 0.25) ( 0, 0, -1, 0.33, 0.33, 0.33) ( 0, 0, 0, -1, 0.5, 0.5) ( 0, 0, 0, 0, -1, 1)
Second question - Say I am only really interested in one contrast, for example between A1*B1 and A1*B2. Is there anything stopping me doing this? I get the impression you need to create the full matrix but I have not read anywhere that it is a must? I'm using jmp and it allows me to run a single contrast I'm just not really sure if it is ok statistically?