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Dear Vina, Typically an additive model (i.e. a contrast [1 0 -1], or just including a 0/1/2 covariate) will give you the most sensitive inferences. But if you want to test your 3-level (genotypic) model for a monotonic effect, the only way to do it is by a conjunction of two contrasts [1 -1 0] and [0 1 -1] You can do this with contrast masking in Feat. -Tom On Tue, Jul 29, 2008 at 2:59 AM, Vina Goghari <[log in to unmask]> wrote: > Hi everyone, > I searched the archives for this topic and I did not see it, so I apologize > if it is a repeat. My question is what is the best way to do an analysis in > three groups, where you want an analysis where Group 1 > Group 2 > Group 3, > as my question has to do with genetic load, which I think will affect brain > activity. > > Thanks, > Vina > > -- ____________________________________________ Thomas Nichols, PhD Director, Modelling & Genetics GlaxoSmithKline Clinical Imaging Centre Senior Research Fellow Oxford University FMRIB Centre