Hi there,
I am currently working through the linear mixed effects example for hippocampal volume on the wiki and I can't quite get my head around how the contrast matrix is set up.
In the example, the design matrix has 14 columns but the contrast matrix only seems to have 5 (below), could you explain why that is please? And also what hypotheses these three different contrasts are testing?
C = [zeros(3,3) [1 0 0 0 0; -1 0 1 0 0; 0 0 -1 0 1] zeros(3,6)];
At the moment I have a simple design with two groups, 4-5 time points so I have a design matrix with 4 columns (intercept, weeks, group, group*time) and the contrast I am using is [0 0 0 1] to test the interaction term. If I were to add covariates such as age and gender would I simply add two more columns to my design matrix and contrast to look like this...[0 0 0 1 0 0]?
Thanks in advance for your help.
Amanda