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On Mon, Mar 12, 2012 at 11:07 PM, Annchen Knodt <[log in to unmask]> wrote: > Hello Everyone, > > I am analyzing repeated measures data for the first time in SPM8, and I > just wanted to verify that I am doing so properly. We are scanning subjects > 3 times using the same task, and are interested in what areas show > differential responses as a function of time (e.g. Are responses greater at > time 1 than at time 2 and 3?). > In order to test this question, I am using the Second Level: Full > Factorial option. > You should use the flexible factorial design and specify a subject factor in addition to the time factor. > I specify one factor with three levels (time, at visit one, two, and > three). Under “Independence” I select “No” because it is a within-subject > design. I then specify three cells, and enter the contrast images from my > first level analyses for time 1 into the Level 1 cell, the con images from > time 2 into the Level 2 cell, and the con images from time 3 into the Level > 3 cell. > After design specification, and estimation, I create the following > contrasts: > In order to test what areas show a main effect of task across all 3 times, > I create an F contrast: > 1 0 0 > 0 1 0 > 0 0 1 > Once you add subjects, you will need to add zeros over the subject columns and the contrast would be: 1 -1 0 0 1 -1 Your contrast tests whether any time is significant, not if there are differences across time. The main effect of task/time is the difference across tasks/times. > In order to test which areas show a significantly different response at > different times, I create an F contrast: > 2 -1 -1 > -1 2 -1 > -1 -1 2 > > This is redundant to the main effect. > Am I analyzing the data correctly in order to test my question? Also, are > the F contrasts I am creating appropriate for those questions? Any feedback > you would be able to provide would be appreciated. Thanks in advance. > > Annchen Knodt > > ~~~~~~~~~~~~ > Annchen Knodt > Graduate Student > Computational Biology & Bioinformatics Program > Laboratory of Neurogenetics > Duke University >