Hi Silvia,

qdec does not support any longitudinal analysis (only cross sectional). So I assume you either compare groups cross sectionally (e.g. at baseline) or you constructed your own longitudinal measure (e.g. percent change, within each subject) and then do a cross sectional analysis of that statistic? Both these things should work. I think your qdec table is setup incorrectly?

Best, Martin

On Tue, 2011-07-19 at 12:45 +0200, Silvia Juanes wrote:

Dear all, We are preprocessed our data to perform a longitudinal study using longitudinal pipeline of Freesurfer 4.5. However, when we try to do the group-analysis using qdec (Freesurfer 5.1), we obtain the following error:

ERROR: QdecGlmDesign::GenerateContrasts: factor 1 must have 2 levels ninputs = 64 Checking inputs nframestot = 64 Allocing output Done allocing nframes = 64 Writing to /home/barbara/subjects/qdec/Untitled/y.mgh gdfReadHeader: reading /home/barbara/subjects/qdec/Untitled/qdec.fsgd INFO: gd2mtx_method is dods Reading source surface /home/barbara/subjects/fsaverage/surf/lh.white ERROR: no contrasts specified. Error in Analyze: command failed: mri_glmfit --y /home/barbara/subjects/qdec/Untitled/y.mgh --fsgd /home/barbara/subjects/qdec/Untitled/qdec.fsgd dods --glmdir /home/barbara/subjects/qdec/Untitled --surf fsaverage lh

Has anyone experienced a similar problem and is there any way to correct it?

Best,

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