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Dear SPMers, I have 3 groups of subjects (A and B are patient groups, and C is healthy control) and I want to know if brain activations to a sensory stimulation are different among the 3 groups, and if so, where the difference comes from (A vs. B, B vs. C or A vs. C). However, subjects had different perceptual ratings to the same sensory stimulus, and these ratings per se affect brain activation. My first question is: I should perform an ANCOVA analysis using perceptual rating as a covariate, and then do subsequent post-hoc between-group pair comparisons. Am I right? In SPM5, I chose “second-level analysis” and “Full factorial design.” The name of “Factor” was “Group,” with 3 levels. Then I specified 3 cells: scans from group A were labeled as level 1, B as level 2, C as level 3. Then, there is an “ANCOVA” under the menu “Factor”. My second question is: should I make it “Yes?” After doing that, under the main “Design” manu, I entered the “Vector”(individual perceptual rating scores) and “Name” (“Rating”) in the “Covariates” item. Then I run it and got results of “main effect of group” and pair comparison contrasts. My third question is: is my procedure right? My final question: what I’ve done is called “one-way ANOVA with post-hoc comparisons,” or “one-way ANCOVA with post-hoc comparisons,” or something else? By the way, should I choose “Flexible factorial” rather than “Full factorial”? Thanks a lot!