Hi - the fslroi, fslmerge and fslsplit programs are very simple, so it
seems unlikely that there is a bug in them. Are you absolutely sure
about exactly what commands you're typing in this?
More comments below....
On 28 Oct 2008, at 18:09, Agnieszka Burzynska wrote:
> Dear all,
>
> I would like to correlate a behavioral measure with FA values on tbss
> skeleton. I wanted to do it for 2 subgroups of my sample separately,
> but
> I am not able to split the all_FA_skeletonized file (here I am
> referring to
> my email "Fslroi on all_FA_skeletonised - output does not match the
> input").
>
> In case you have an idea how to overcome the problem, I will be very
> grateful.
>
> In meantime I wanted to run some analyses with a design matrix for all
> subjects together.
>
> Here are some of my designs and I wanted to ask if they make sense
> the way i
> describe them (I read previous posts but I am still not sure what is
> the
> best to answer my questions). Unfortunately I have no experience
> with FEAT
> design matrices, hence these basic questions.
>
> As I mentioned before, I have 2 subgroups (younger and older), in
> designs
> below first 3 entries belong to 1 group, the remaining 3 to the other.
>
> 1) How BEH correlates with FA in the whole sample?
>
> Group EV1(beh, demeaned values)
> 1 -1
> 1 -3
> 1 -5
> 1 3
> 1 1
> 1 5
>
> Contrast : -1 (I expect negative correlation)
>
> Randomise with -D option
Sure - looks fine.
>
>
> Or if the two subgroups have different means for BEH, should I split
> EV1
> into two Evs:
> EV1 Ev2
> -1 0
> -3 0
> -5 0
> 0 3
> 0 1
> 0 5
> And then skip -D?
Not quite - you need to demean each groups values before padding with
zeros. And you DO need the -D option.
>
>
> 2) How BEH correlates with FA after regressing out for age?
>
> Group EV1(beh, demeaned values) EV2 (AGE, demeaned)
> 1 -1 -12
> 1 -3 -10
> 1 -5 -7
> 1 3 12
> 1 1 7
> 1 5 10
>
> contrasts: -1 0
> Randomise with -D (as there is no EV that models the mean)
Fine.
>
>
> Or would it make more sense to orthogonalize EV1 with respect to EV2
> by
> clicking it in Glm_gui? (if I know that BEH and age are not highly
> correlated?)
You can also do that - depends on what you want the model to do.
>
>
> 3) How FA correlates with BEH, after regressing out for agegroup to
> which a
> subject belongs?
>
> Group EV1 (young) EV2 (old) EV1(beh, demeaned values)
> 1 1 0 -1
> 1 1 0 -3
> 1 1 0 -5
> 2 0 1 3
> 2 0 1 1
> 2 0 1 5
>
> Contrasts 0 0 -1
> 1 -1 0 (where younger have higher FA than older, after regressing
> out for
> BEH?)
> Having EV1 and EV2 that model the mean, I dont need to add -D
> option. Is it
> correct?
Correct
>
>
> 4)
> Group EV1(age, demeaned values) EV2 (BEH young, demeaned) EV3(BEH
> old)
> 1 -1 -12 0
> 1 -3 -10 0
> 1 -5 -7 0
> 1 3 0 12
> 1 1 0 7
> 1 5 0 10
>
> Contrast 0 1 -1 (would it tell me where BEH correlates with FA
> higher in
> young than old adults, after regressing out for age?)
Yes but as above you need to demean the sub-group values before
padding with zeros
>
>
> 5) or would it be more meaningful to make an interaction analysis
> (Beh and
> age interaction) using F-tests? If yes, how should it look like?
No - I would use the above examples.
Cheers.
>
>
>
> Thank you very much for help in advance,
> Best,
> Aga
>
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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)
[log in to unmask] http://www.fmrib.ox.ac.uk/~steve
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