Dear list,

I have a question re group comparisons. I have one group factor with three levels. I have done group-wise comparisons with these groups using qdec (ie doing pairwise comparisons, as it only allows group comparisons between two groups as far as I am aware?) as well as using mri glm fit, specifying the contrast as 1 0 -1 to compare two groups without the effect of the other third group being included. I have found that I get different results for these two methods; using mriglmfit I get no vertices surviving multiple comparisons, whilst I get several using qdec. Could this be because of the differences in using FDR/monte carlo simulation or does it point towards a bigger problem, for example me doing something wrong at some stage? Or is there another explanation?

Very grateful for prompt response and help,

Cheers,

Melinda