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THanks for your answers. I have three covariates that are 3 different scores related to each other. i.e. cov_2 is the same test than cov_1 with an added cognitive component. Therefore I wanna determine the functional connectivity associated to that added cognitive component. Can I use thus their relationship [1 -1] on my experimental model? What is that output telling? Covariates are scaled and coverted to a Z-score.

So you say I could use independent experiments, convert the output to a Z-score and subtract the Z-map of cov_1 from Z-map of cov_2?

 --
Manuel Garcia-Garcia, PhD
Postdoctoral Fellowship
Phyllis Green and Randolph Cowen Institute for Pediatric Research
NYU Child Study Center
Phone: +1 (212) 263 4736
e mail: [log in to unmask]
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USA
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On Fri, Aug 19, 2011 at 10:02 AM, MCLAREN, Donald <[log in to unmask]> wrote:
It sounds like your doing a linear regression with functional connectivity as your dependent measure and three covariates (e.g. age, memory, attention). 

If this is the case, then:
(1) What does a difference (slope of age > slope of memory) between covariates tell you? 
(2) If you want to compare the slopes, you need to make sure all your covariates are on the same scale. The easiest is to convert each covariate to a Z-score.
(3) Are you wanting to compare their slopes or just which regions are correlated with the covariate? You could convert the relationship of each [1] or [-1] one to a Z-score and just subtract the Z-maps to test if the relationships are different (not just the slopes).



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, Aug 18, 2011 at 4:22 PM, Manuel Garcia-Garcia <[log in to unmask]> wrote:
Hello,

I was wondering if anyone has some thoughts on how to
perform a Group-level analysis to contrast covariates of interests
(within one group). I want to contrast the effect of 3 different scores
(which are not independent from each other) on functional connectivity.
Does anyone have any thought on how to do it?

Thanks!

--
Manuel Garcia-Garcia, PhD
Postdoctoral Fellowship
Phyllis Green and Randolph Cowen Institute for Pediatric Research
NYU Child Study Center
Phone: +1 (212) 263 4736
e mail: [log in to unmask]
215 Lexington Ave, 14th Floor
New York, NY 10016
USA
*****************************************************************************************
Sign up for a superb 5-day scientific program on Cognitive Neuroscience <http://www.icon11mallorca.org/index.php>  in
the beautiful island of Mallorca, including:
  • 9 keynote speakers <http://www.icon11mallorca.org/keynote.php>
  • 24 symposia <http://goog_120504725>  (100+ contributors) <http://www.icon11mallorca.org/symposia.php>
  • 500+ poster presentations <http://www.icon11mallorca.org/posters.php>
  • 750+ scientists and professionals already registered
*****************************************************************************************