On Tue, Aug 7, 2012 at 7:27 AM, Maren Strenziok
<[log in to unmask]> wrote:
> Hi Donald,
>
> thanks for you reply. What you describe gets me to the effect of time. What
> do you suggest to get to the effect of group (and interaction effect) if I
> have unequal numbers of subjects in each group?
For the interaction, use a two-sample t-test.
For the group effect, you need to average time1 and time2 instead of
subtracting them.
>
> Maren
>
>
> On Fri, May 25, 2012 at 11:54 AM, MCLAREN, Donald <[log in to unmask]>
> wrote:
>>
>> On Fri, May 25, 2012 at 10:24 AM, Maren Strenziok
>> <[log in to unmask]> wrote:
>>>
>>> Hi Tom,
>>>
>>> after you laid out the 2x2 ANOVA design in a post a few weeks ago, I
>>> tried it out and wonder what your opinion is on the following situation. I
>>> have scans from two groups (trained, non-trained) and two time points
>>> (pre-training, post-training). Although each subject has a pre- and a
>>> post-training scan, I have unequal numbers of subjects in my groups (10,
>>> 12). So when I prepare the difference map required to look at the effect of
>>> group, following your logic, I would first add the map of group A at time
>>> point 1 and group A at time point 2, then add map B at time 1 and map B at
>>> time 2. If I do that I get two files with different volume numbers as group
>>> A has only 10 subjects and group B has 12. When I now subtract these maps
>>> from each other, the result is a difference map that consists of 10 volumes.
>>
>>
>> I'm not quite sure I follow what you did, but what you should end up with
>> after subtracting time1 from time2 is 22 volumes (1 for each subject).
>> Essentially, for each subject, you subtract the two time points and get a
>> difference image. Then you put those difference images into a two-sample
>> t-test (10 in one group, 12 in the other group).
>>
>>
>>>
>>> Which part of my data was omitted here? The last 2 subjects of group two?
>>> Is this good practice or should I try something else? Also, to complicate
>>> things, I have DTI data that I submitted to the tbss processing stream in
>>> FSL. So in addition to a map with data, I also need a mask file which I
>>> would make from the pooled group I guess. Can you let me know whether the
>>> FEAT GUI to set up the design and matrix files is the better option in my
>>> case?
>>>
>>> Any comments are highly appreciated.
>>>
>>> Maren
>>>
>>> On Tue, May 15, 2012 at 6:00 PM, Thomas Nichols
>>> <[log in to unmask]> wrote:
>>>>
>>>> Dear Ciara,
>>>>
>>>> Repeated measures, if you read the list, is quite tricky. Really the
>>>> best thing is to eliminate any repeated measures and run separate analyses
>>>> for each contrast of interest. I.e. If the design is
>>>>
>>>> A1 A2 B1 B2
>>>>
>>>> then compute the effects for each subject with fslmaths:
>>>>
>>>> Main effect of A vs B: (A1+A2)-(B1+B2)
>>>> Main effect of 1 vs 2: (A1+B1)-(A2+B2)
>>>> Interaction: (A1-A2)-(B1-B2)
>>>>
>>>> Then you'll have reduced your data to a set of 24 images which you can
>>>> submit to a one-sample t-test.
>>>>
>>>> Does this help?
>>>>
>>>> -Tom
>>>>
>>>>
>>>> On Tue, May 15, 2012 at 7:16 PM, Ciara Greene <[log in to unmask]>
>>>> wrote:
>>>>>
>>>>> Hi FSL users,
>>>>>
>>>>> I'm a bit confused as to how to go about implementing a 2x2 repeated
>>>>> measures design in randomise.
>>>>>
>>>>> I have resting state data from 24 subjects under 4 conditions - 2
>>>>> factors, each with 2 levels - each of which was acquired in a separate run.
>>>>> I have conducted concat ICA on this data and now want to compare ICs across
>>>>> the different scanning conditions using dual regression. I understand that
>>>>> implementing repeated measures designs in randomise can be tricky; is there
>>>>> a way to extend the 1 factor/4 levels design described at
>>>>> http://www.fmrib.ox.ac.uk/fsl/randomise/index.html#Ex:RepeatMeas to examine
>>>>> main effects of factor 1 and factor 2 and their interaction?
>>>>>
>>>>> Thanks for your help,
>>>>> Ciara
>>>>
>>>>
>>>>
>>>>
>>>> --
>>>> __________________________________________________________
>>>> Thomas Nichols, PhD
>>>> Principal Research Fellow, Head of Neuroimaging Statistics
>>>> Department of Statistics & Warwick Manufacturing Group
>>>> University of Warwick, Coventry CV4 7AL, United Kingdom
>>>>
>>>> Web: http://go.warwick.ac.uk/tenichols
>>>> Email: [log in to unmask]
>>>> Phone, Stats: +44 24761 51086, WMG: +44 24761 50752
>>>> Fax: +44 24 7652 4532
>>>>
>>>>
>>>
>>
>
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