Hi Donald,
Why do you say that it would probably be ok to not model and account for
familial relationships? There are already emerging reports that
measures of functional brain connectivity are heritable. (Smit, Behav
Genet, 2010; Glahn, PNAS, 2010).
cheers,
-MH
On Wed, 2011-07-27 at 19:15 +0100, MCLAREN, Donald wrote:
> Not including family information would probably be okay as you could
> argue that the subjects are different and they were selected to be
> different from one and other.
>
>
> The sessions are not independent and not modelling session would be a
> violation of the statistical assumptions.
>
>
> Now if you have session in the model, then the group and/or covariate
> terms are invalid because of the wrong error term.
>
>
> Randomise won't really help in this case, because the exchangeability
> you need is between high/low not session1/session2.
>
>
> We might have a solution via SPM that we are testing and was the basis
> of my poster at HBM. Not sure if it would work in this case. I'm
> emailing a colleague to see if he has a solution.
>
> 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 Wed, Jul 27, 2011 at 11:44 AM, Diederick Stoffers
> <[log in to unmask]> wrote:
> Hi guys,
>
>
> Thanks for the advice. Averaging over twin pairs is not really
> an option, the twins were specifically selected because they
> were discordant on a certain psy scale. I could average over
> sessions, but am hesitant to do so as the behavioural measure
> I am interested in can be quite different over sessions; i
> would lose a lot of power in my group comparison.
>
>
> If I were to go about this a different way; I would just do a
> regression of fMRI activation over all sessions versus the
> behavioural measure without including any information about
> family ties or session and not averaging. I will lose some
> power because I am not moddelling family ties and sessions,
> but will gain by having more observations.
>
>
> A little extra background, this is actually resting-state data
> on which I performed concatenated ICA and now want to do dual
> regression and compare the resulting 160 spatial maps (80
> subjects * 2 sessions) using randomise. Will the results be
> valid if I don't include information on the dependencies?
>
>
> Cheers,
>
>
> Diederick
>
>
>
>
> On 26 jul. 2011, at 20:28, Michael Harms wrote:
>
> > Hi Diederick,
> > To my knowledge (someone please correct me if I'm wrong),
> > there aren't any
> > packages currently that can easily construct voxel-based
> > maps in the
> > context of the complicated variance relationships that one
> > might want to
> > model for sibling and/or twin studies. However, if you have
> > ROI-based
> > data, you can import it into a package that allows one to
> > specify
> > covariance structures between subjects in a sibling pair,
> > such as SAS's
> > PROC MIXED. I'm sure that R and SPSS have something
> > equivalent as well.
> >
> > cheers,
> > -MH
> >
> >
> > > You need to eliminate the repeated measurements.
> > >
> > > The issue is that if you have between-subject effects and
> > > within-subject
> > > effects in the same model, then you only investigate the
> > > within-subject
> > > effects because the error term is for the within-subject
> > > effects. Once
> > > software becomes available to have multiple error terms
> > > for the between
> > > and
> > > within-subject effects, then you'll not need to collapse
> > > them.
> > >
> > > Additionally, if you have more then one within-subject
> > > effect, then you
> > > can
> > > only look at the interaction for the same reason.
> > >
> > > Given these points, it seems that it would be best to
> > > collapse (e.g.
> > > average
> > > your two conditions) to eliminate the repeated
> > > measurement.
> > >
> > > I'm not sure how you should deal with the twins not being
> > > independent. I
> > > would say average each twin pair, but that seems like it
> > > would ruin your
> > > research question.
> > >
> > >
> > > 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
> > > =====================
> > > This e-mail contains CONFIDENTIAL INFORMATION which may
> > > contain PROTECTED
> > > HEALTHCARE INFORMATION and may also be LEGALLY PRIVILEGED
> > > and which is
> > > intended only for the use of the individual or entity
> > > named above. If the
> > > reader of the e-mail is not the intended recipient or the
> > > employee or
> > > agent
> > > responsible for delivering it to the intended recipient,
> > > you are hereby
> > > notified that you are in possession of confidential and
> > > privileged
> > > information. Any unauthorized use, disclosure, copying or
> > > the taking of
> > > any
> > > action in reliance on the contents of this information is
> > > strictly
> > > prohibited and may be unlawful. If you have received this
> > > e-mail
> > > unintentionally, please immediately notify the sender via
> > > telephone at
> > > (773)
> > >
> > > 406-2464 or email.
> > >
> > >
> > >
> > > On Tue, Jul 26, 2011 at 3:31 PM, Diederick Stoffers
> > > <[log in to unmask]>wrote:
> > >
> > > > Hi all,
> > > >
> > > > I have a group of 80 subjects (all dizygotic twins) from
> > > > whom I have two
> > > > fMRI measurements per subject. For all these subjects I
> > > > also have a
> > > > behavioural score per scan. I would like to compare
> > > > scans associated
> > > > with a
> > > > high score with those with a low score, while correcting
> > > > for the fact
> > > > that
> > > > measurements in dizygotic twins are not independent and
> > > > measurements in
> > > > the
> > > > same subject are not independent. For now, I am not
> > > > interested in
> > > > within-subject effects over scans.
> > > >
> > > > I have been thinking how to best model this, but quite
> > > > frankly I can't
> > > > wrap
> > > > my head around it and I wasn't able to deduce this from
> > > > the mailing list
> > > > or
> > > > FSL site. Could anyone shed some light on how to set up
> > > > my design
> > > > matrix?
> > > >
> > > > Thanks,
> > > >
> > > > Diederick
> > > >
> > >
>
>
>
>
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