Apologies if this is already answered on the list, I found this question posted a couple times but without a response.
I have a GLM with 9 conditions. Three of these conditions increase parametrically so I'd be using a contrast vector [1 2 3 zeros(1,6)]; however i believe that t-contrasts are supposed to sum to zero so I'm not sure this contrast vector is correct. If you sum these to zero then you get [-1 0 1 zeros(1,6)]; which also doesn't seem right.
How important is it that t-contrasts sum to zero? and if it is important what's the appropriate contrast for an odd number of linearly increasing conditions?
Thanks in advance