<
[log in to unmask]> wrote:
>
> Dear Donald,
>
> Thank you for your reply.
>
> So if I understand correctly my design is correct, just in order to show constant linear decrease I should add contrast as below:
>
> Group EV1 EV2 EV3 EV4 EV5
> EV6 EV7
> subj1 subj2 time1 time 2 time 3
> time 4 time5
> 1 1 0 1 0
> 0 0 0
> 1 0 1 1 0
> 0 0 0
> 1 1 0 0 1 0
> 0 0
> 1 0 1 0 1 0
> 0 0
> 1 1 0 0 0
> 1 0 0
> 1 0 1 0 0
> 1 0 0
> 1 1 0 0 0
> 0 1 0
> 1 0 1 0 0
> 0 1 0
> 1 1 0 0 0
> 0 0 1
> 1 0 1 0 0
> 0 0 1
>
> Contrasts EV1 EV2 EV3 EV4 EV5
> EV6 EV7
> A-B 0 0 1 -1
> 0 0 0 ( shows decrease FA between timepoint
> 1&2)
> B-C 0 0 0 1
> -1 0 0
> C-D 0 0 0 0 1
> -1 0
> D-E 0 0 0 0
> 0 1 -1
> A-B-C-D-E 0 0 2 1 0 -1 -2
>
> Is it right?
>
> Again thank you for your kind help.
>
> Regards,
>
> Gelareh
>
> On Sat, Jan 22, 2011 at 3:41 PM, MCLAREN, Donald <
[log in to unmask]> wrote:
>
> A constant linear decrease doesn't not mean A>B>C>D>E; rather on
> average there is a constant decrease across time. If you want the
> stated equation, then you need to form a conjunction.
>
> Typically, a constant linear decrease for 5 repetitions would be
> defined as 2 1 0 -1 -2. The caveat is that this contrast could be
> driven by A and E, but it would still be considered linear across
> time.
>
> Hope this helps.
>
> Best Regards, Donald McLaren
> =================
> D.G. McLaren, Ph.D.
> Postdoctoral Research Fellow, GRECC, Bedford VA
> Research Fellow, Department of Neurology, Massachusetts General
> Hospital and Harvard Medical School
> Office: (773) 406-2464
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>
> On Thu, Jan 20, 2011 at 11:55 PM, Gelareh Ahmadi
> <
[log in to unmask]> wrote:
>> Dear FSL experts,
>>
>> My question is about designing GLM for repeated measure ANOVA.
>>
>> I have FA images from DTI scans for my subjcets. Each subject scanned in 5 different time points.
>>
>> I want to design a GLM which shows areas with decreased FA between time point 1&2, 2&3, 3 &4 , 4&5 and also areas which shows linear decrease from time point 1 to time point 5.
>>
>> I think for my first goal I should use ANOVA (1 factor-5 level), therefore for instance, for 2 subjects having scan in 5 time points, in order to show decrease FA between timepoint A&B, B&C, C&D and D&E, I should design:
>>
>> Group EV1 EV2 EV3 EV4 EV5 EV6 EV7
>> subj1 subj2 time1 time 2 time 3 time 4 time5
>> 1 1 0 1 0 0 0 0
>> 1 0 1 1 0 0 0 0
>> 1 1 0 0 1 0 0 0
>> 1 0 1 0 1 0 0 0
>> 1 1 0 0 0 1 0 0
>> 1 0 1 0 0 1 0 0
>> 1 1 0 0 0 0 1 0
>> 1 0 1 0 0 0 1 0
>> 1 1 0 0 0 0 0 1
>> 1 0 1 0 0 0 0 1
>>
>> Contrasts EV1 EV2 EV3 EV4 EV5 EV6 EV7
>> A-B 0 0 1 -1 0 0 0 ( shows decrease FA between timepoint 1&2)
>> B-C 0 0 0 1 -1 0 0
>> C-D 0 0 0 0 1 -1 0
>> D-E 0 0 0 0 0 1 -1
>>
>> But I have no idea how I can show there is constant linear decrease from time point 1 to timepoint 5 ? I mean showing that FA1>FA2>FA3>FA4>FA5.
>>
>> I would highly appreciate if any one could let me know if Iam correct for the first goal and how I can solve my second problem.
>>
>> Best Regards,
>>
>> Gelareh
>>
> --
> Gelareh Ahmadi, MD
> PhD Candidate
> Neuroimaging Group
> Howard Florey Institute
> University of Melbourne
> VIC, Australia, 3010
>
> ph +61 3 8344 1904
> fax +61 3 9347 0446
>