Hi,
1. It seems likely that the WM response to cocaine-per-day and cocaine-
years will be somehow correlated; I would start with a simpler model
first to see if you get anything, for example, multiplying EVs 2 and 3
together.
2. You should just use the version of randomise in FSL4.0, which
doesn't have the -x option, and just use the design in your question
1. below, which automatically takes care of the 'confounds' relative
to any given contrast.
3. See above - just use model 1 (simplifed as I described above) with
FSL 4.0 - it is all taken care of for you!
Cheers.
On 20 Feb 2008, at 13:16, Jiansong Xu wrote:
> Dear Friends:
>
> I'm using TBSS to assess correlations (both positive and negative)
> between FA and age, years of cocaine use, amount of cocaine use per
> day, and years of alcohol use of 16 cocaine abusers. So, I have 4
> variables (EVs). I will demean every variable first.
>
> I'm wondering if following design and contrast are correct.
>
>
> 1. First Procedure:
>
> Design:
>
> EV1 EV2 EV3 EV4
> age coca-y coca-d alco-y
> ..........
>
>
> Contrast
>
> 1 0 0 0
> -1 0 0 0
> 0 1 0 0
> 0 -1 0 0
> 0 0 1 0
> 0 0 -1 0
> 0 0 0 1
> 0 0 0 -1
>
>
> 2. Second Procedure
>
> Assume I want to assess the correlation between FA and age only, I
> also want to eliminate the confounds of other three variables such
> as years of cocaine use. I will use following design:
>
> First matrix:
>
> EV1
> age
> ...
>
> Contrast
> 1
> -1
>
> Second matrix (after -x)
>
> EV1 EV2 EV3
> coca-y coca-d alco-y
>
>
> 3. Assume I want to assess the correlations between FA and each of
> the four variables, and also eliminate the confounds of other three
> variables for each assessed variable. Do I have to repeat the above
> procedure 2 four times? Are there any better methods than repeat
> procedure 2 four times?
>
>
>
> Best
>
> Jiansong Xu, M.D., Ph.D.
> Associate Research Scientist
> Dept. of Psychiatry
> Yale School of Medicine
>
> Connecticut Mental Health Center, Room S-100
> 34 Park St.
> New Haven, CT 06519
>
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Stephen M. Smith, Professor of Biomedical Engineering
Associate Director, Oxford University FMRIB Centre
FMRIB, JR Hospital, Headington, Oxford OX3 9DU, UK
+44 (0) 1865 222726 (fax 222717)
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