Hi Aldo, this ok to me.
doug
On 12/09/2013 04:53 AM, Aldo Cordova wrote:
> Dear FreeSurfer experts,
>
> I'm trying to implement the steps you indicate in the Paired Analysis'
> wiki site, but I still don't get something:
> In this site, you show the next FSGD file:
> GroupDescriptorFile 1
> Class Main
> Variables Age
> Input subject1pair Main 30
> Input subject2pair Main 40
> Input subject3pair Main 50
> Input subject4pair Main 60
>
> Accordingly, "Age" is a variable whose value is the same for each pair
> of subjects (i.e., it is a measure of between-pair differences, but
> does not contain information about differences found in subjects of
> the same pair). Nevertheless, I need to introduce some covariates of
> interest whose value would indicate within-pair differences (i.e., the
> difference between "subjectN" and "subjectNmatch", where "N" is the
> arbitrarily assigned pair number). I made the next FSGD, but I'm
> wondering it's not correct (is it?):
>
> GroupDescriptorFile 1
> Title trait1_trait2_paired
> MeasurementName thickness
> Class male
> Class female
> Variables Age trait1_diff trait2_diff
> Input subject1pair female 24 150 1850
> Input subject2pair male 41 -200 -2090
> Input subject3pair female 48 50 -6508
> Input subjec4tpair male 53 -100 -7100
> Input subject5pair female 36 150 1950
> .
> .
> .
>
>
> In this FSGD, the last two variables ("trait1_diff" and "trait2_diff")
> would represent within-pair differences. As you can see, there are
> both positive and negative values, depending on the random order of
> individuals within a pair. Afterwards, contrast files such as "0 0 0 0
> 0.5 0.5 0 0" or "0 0 0 0 0 0 0.5 0.5" would be used to check whether
> "trait1_diff" or "trait2_diff" have an effect on cortical thickness,
> regressing out the effects of "gender", "Age" and either "trait2_diff"
> or "trait1_diff".
>
> Could you please tell me if the FSGD table is correct? If it isn't,
> how to implement such an approach? (I.e., how to use both between-pair
> and within-pair variables?) Also, are the contrast files mentioned
> above correct?
>
> Thank you in advance,
> Aldo
>
>
>
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--
Douglas N. Greve, Ph.D.
MGH-NMR Center
gr...@nmr.mgh.harvard.edu
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