Hi FSL,
I found this old answer saying that to test a linear trend across three groups the correct contrast is -1 0 1.
That is the same contrast for testing the difference between the two groups, which to me means the data in the middle group is simply ignored, which I think means that this middle group could be higher or lower than both other groups, which is not really within the spirit of seeing if a linear trend holds across the three groups.
Is there any way to test this more stringent "linear trend across three groups and the middle group is intermediate" idea with a simple statistical test in FSL?
Thanks,
Dan
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