Hi Ana,

A simple design to test the ordering of time1 > time2 > time3 is to use a design matrix with two columns: Column 1 is filled with ones; Column 2 contains a 1 for time point 1, 2 for time point 2 and 3 for time point 3. Additional columns are needed to model the within-subject (repeated measures) effects. These would be the same the previous design. The contrast for a t-test would be [0 1 0 0 0...] and [0 -1 0 0 0...]. The first contrast tests t1 > t2 > t3, while the second contrast tests t1 < t2 < t3.

Note that this is a very simple design and assumes a linear increases (or decrease) over time, as well as other assumptions. There are more advanced models available that you might want to investigate.

If the gap between t1 and t2 is smaller than the gap between t2 and t3, you can put a value higher than 3 in the design matrix for time point 3.

Andrew


Originally posted by Ana Coelho: