Glad to hear that reprocessing wasn't a big deal. It was the right
thing to do.
Now you can just to the "Single-Group Average (One-Sample T-Test)"
higher-level modeling.
http://www.fmrib.ox.ac.uk/fsl/feat5/detail.html#SingleGroupAverage
We will end up with cope{1,2,3}.feat directories within the
resulting .gfeat directory, and the stats contained in each of those
will tell you whether that particular cope differed significantly from 0
across your subjects.
As an aside, note that lower level EVs are NOT "groups" and are not
related to "groups" in any meaningful sense of the word. Talking about
first level copes as "group differences" and "group copes" is highly
confusing.
cheers,
-MH
On Wed, 2011-09-21 at 15:07 -0400, Leslie Engineering wrote:
> Ok I took your advice and reprocessed! :) ... you were pushy!
>
>
> Not to beat a dead horse, but since I had two evs in the individual
> subject models and contrasts (1,-1)(-1,1)(1,1), can I do essentially a
> single group analysis. Won't the group differences be embedded in
> three group copes?
>
> On Tue, Sep 20, 2011 at 12:57 PM, Michael Harms
> <[log in to unmask]> wrote:
> Is it really that much effort to re-run the lower-level
> analyses? It is
> just processor time :)
>
> My bias would be to say that no, what you want to do is
> unfortunately
> not ok, unless you can establish equivalence by testing both
> approaches
> in a subset of subjects.
>
> cheers,
> -MH
>
>
> On Tue, 2011-09-20 at 12:47 -0400, Leslie Engineering wrote:
> > Thanks. Yes it is only one group. There isn't necessarily a
> > correlation between EV1 and EV2 so I was trying to bypass
> redoing the
> > lower-level analysis. I guess I just wanted to know if you
> thought
> > that was ok?
> >
> >
> > On Tue, Sep 20, 2011 at 12:19 PM, Michael Harms
> > <[log in to unmask]> wrote:
> > I'm confused by your usage of the term "groups". Do
> you
> > actually have
> > two groups of subjects that you are trying to
> contrast on a
> > given lower
> > level contrast?
> >
> > Or are you simply trying to figure out a way to
> effect the
> > equivalent of
> > a (1,-1) contrast that should have been included in
> the 1st
> > level, but
> > wasn't? If this is the case, then it all depends on
> the
> > degree of
> > correlation of EV1 and EV2, as I noted when you
> inquired about
> > this
> > previously
> > https://www.jiscmail.ac.uk/cgi-bin/webadmin?
> > A2=ind1109&L=FSL&P=R16891&1=FSL&9=A&J=on&d=No+Match%
> 3BMatch%
> > 3BMatches&z=4
> >
> > The "proper" way to do this is to redo the lower-
> level
> > modeling with
> > (1,-1) included as a contrast. As a general matter,
> desired
> > contrasts
> > should be included in the first level modeling so
> that you
> > properly
> > account for the correlation between EVs.
> >
> > cheers,
> > -MH
> >
> >
> >
> > On Tue, 2011-09-20 at 11:55 -0400, Leslie
> Engineering wrote:
> > > I think you misunderstand. The last question was
> in regard
> > to 1 group
> > > that individual subjects were run with EV1 and EV2
> > paradigms.
> > > Unfortunately I ran contrasts (1,0) (0,1) (1,1).
> But, now I
> > want to
> > > see activation differences between EV1 and EV2.
> This would
> > have been
> > > straight forward had my contrasts been (1,-1) and
> (-1,1) (i
> > believe).
> > > But, since I don't have that, may I run each
> subject twice
> > and
> > > consider the EV1s and EV2s different groups so I
> don't have
> > to rerun
> > > the individuals with the proper contrasts?
> > >
> > >
> > > Thanks
> > >
> > > On Tue, Sep 20, 2011 at 11:50 AM, Michael Harms
> > > <[log in to unmask]> wrote:
> > > To compare groups you need to run a
> "Higher-level
> > analysis" in
> > > FEAT
> > > using the lower-level FEAT directories as
> inputs.
> > This will
> > > then create
> > > a group contrast for each of your lower-
> level
> > copes. Assuming
> > > that you
> > > have already created the desired lower-
> level copes
> > at the
> > > individual
> > > level, then no, you don't have to rerun
> individuals.
> > >
> > > cheers,
> > > -MH
> > >
> > >
> > > On Tue, 2011-09-20 at 11:38 -0400, Leslie
> > Engineering wrote:
> > > > Or can I just treat them as two separate
> groups so
> > i don't
> > > have to
> > > > rerun individuals?
> > > >
> > > > On Tue, Sep 20, 2011 at 11:36 AM, Leslie
> > Engineering
> > > > <[log in to unmask]> wrote:
> > > > So I am a little confused, then.
> If i have
> > > individual subjects
> > > > that were run with two EVs
> contrasts (1,0)
> > (0,1)
> > > (1,1), do I
> > > > have to go back and rerun each
> individual
> > subject
> > > with
> > > > contrasts (1,-1)(-1,1) in order
> to get
> > group
> > > differences or
> > > > can I manipulate these in some
> way?
> > > >
> > > > On Tue, Sep 20, 2011 at 11:14
> AM, Michael
> > Harms
> > > > <[log in to unmask]> wrote:
> > > > Group contrasts (and
> statistics)
> > should be
> > > calculated
> > > > from the
> > > > appropriate copes, not
> done "post-
> > hoc" by
> > > subtracting
> > > > z-maps.
> > > >
> > > > See
> > > >
> > >
> >
> http://www.fmrib.ox.ac.uk/fsl/feat5/detail.html#UnpairedTwoGroupDifference
> > > > which provides a clear
> example of
> > how to
> > > proceed.
> > > >
> > > > cheers,
> > > > -MH
> > > >
> > > >
> > > > On Tue, 2011-09-20 at
> 11:07 -0400,
> > Leslie
> > > Engineering
> > > > wrote:
> > > > > does it make a
> difference if
> > instead I
> > > have one
> > > > group that went
> > > > > through a single
> paradigm, EV.
> > If EV is
> > > made up of
> > > > two separate
> > > > > stimuli blocks and I
> want to
> > separate them
> > > into EV1
> > > > and EV2, can I
> > > > > run a single group
> average using
> > EV1 and a
> > > single
> > > > group average using
> > > > > EV2 then subtract the
> z scores
> > for an
> > > activation
> > > > difference between
> > > > > the two stimuli?
> > > > >
> > > > >
> > > > > thanks so much
> > > > >
> > > > > On Tue, Sep 20, 2011
> at 10:08
> > AM, Leslie
> > > Engineering
> > > > >
> <[log in to unmask]>
> > wrote:
> > > > > Hello-
> > > > >
> > > > >
> > > > > I ran two
> separate
> > simple group
> > > average
> > > > analysis. Both groups
> > > > > underwent the
> same fmri
> > scan
> > > sequence.
> > > > Instead of rerunning a
> > > > > group analysis
> and
> > included all
> > > subjects
> > > > from both groups and
> > > > > setting up
> contrasts for
> > group
> > > differences
> > > > (1,-1)(-1,1), is it
> > > > > statistically
> sound to
> > simply
> > > subtract their
> > > > zscores?
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > > >
> > > >
> > > >
> > > >
> > > >
> > >
> > >
> > >
> >
> >
> >
>
>
>
