Hi Tom,
Thank you for the reply. I attached the design files as a .zip. The command
I used for randomise was:
randomise_parallel -i all_FA_skeletonised -o FA -m mean_FA_skeleton_mask -d
design.mat -t design.con -f design.fts -n 1000 --T2 -V
John
On Fri, 6 Mar 2009 08:33:32 +0000, Thomas Nichols <[log in to unmask]>
wrote:
>Dear John,
>
>This does indeed sound funny. Can you upload your mat, con and fcon files,
>along with responding with the precise randomise command you ran?
>
>Thanks in advance!
>
>-Tom
>
>On Thu, Mar 5, 2009 at 8:29 PM, John Colby <[log in to unmask]> wrote:
>
>> Hello all,
>>
>> I am doing a pretty basic 3 group comparison in TBSS, investigating whether
>> there is any group effect on FA. Demeaned age is included as a 4th EV
>> because this is a young population and the groups are not precisely age
>> matched. I entered the 6 pair-wise t-test contrasts for potential future
>> post-hoc examination, and selected 2 of them for an F-test to answer the
>> question, "Are there any areas where FA is significantly different between
>> groups?" See the attached image for my model setup.
>>
>> What I am confused about is this: When age is included as a covariate (as
>> opposed to when it is not), the individual FA_tfce_corrp_tstat maps are
>> more
>> robust, but the overall F-test map (FA_tfce_corrp_fstat) drops almost to
>> zero. This opposite behavior surprised me and makes me think that I might
>> be
>> doing something wrong in my model setup, or perhaps just not fully
>> understanding how F-tests work in FSL. Does this seem like normal behavior,
>> or does it look like I'm doing something wrong? Any help would be
>> appreciated!
>>
>> Randomise runs fine (no errors and all permutations finish). It was called
>> as:
>> randomise_parallel -i all_FA_skeletonised -o FA -m mean_FA_skeleton_mask -d
>> design.mat -t design.con -f design.fts -n 1000 --T2 -V
>>
>> Thanks!
>>
>> John Colby
>>
>> MD/PhD Student
>> Developmental Cognitive Neuroimaging Lab
>> David Geffen School of Medicine at UCLA
>>
>
>
>
>--
>____________________________________________
>Thomas Nichols, PhD
>Director, Modelling & Genetics
>GlaxoSmithKline Clinical Imaging Centre
>
>Senior Research Fellow
>Oxford University FMRIB Centre
>
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