> Date: Tue, 13 Nov 2012 23:21:19 -0500
> From: [log in to unmask]
> Subject: Re: [SPM] contrast vector for paired t-test
> To: [log in to unmask]
>
> I would use GLM Flex or a one-way within-subject ANOVA since you have
> 4 measures per subject.
>
> But to answer your exact question, the contrast to compare C1 to C2
> would be 1 -1 for C1>C2 T-test and -1 1 for C2>C1 T-test. The F-test
> can be 1 -1 or -1 1. Both will be the same. T-tests will test your
> directional hypothesis, the F-test tests for either direction.
>
> Best Regards, Donald McLaren
> =================
> D.G. McLaren, Ph.D.
> Research Fellow, Department of Neurology, Massachusetts General Hospital and
> Harvard Medical School
> Postdoctoral Research Fellow, GRECC, Bedford VA
> Website: http://www.martinos.org/~mclaren
> Office: (773) 406-2464
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>
> On Tue, Nov 13, 2012 at 1:56 PM, Desbot Julie <[log in to unmask]> wrote:
> >
> >
> > Dear SPMers,
> >
> > I have made an experiment where 20 people had to look at fearfull images vs
> > neutral images.
> > Each subject watched the same run 4 times, with 1 parameter varying each
> > time (so in total I have 4 times for the same run). But I can’t compare the
> > 4 sessions together because they differs from the previous one by a single
> > parameter. For instance the 3rd session differs from the 1st one by 2
> > parameters.
> > To see if one parameter has an effect, I have done a paired t-test between 2
> > conditions (time 1 vs time 2 ; time2 vs time 3 ; time 1 vs time 4).
> > First I would like to know if the paired t-test is appropriate and second, I
> > am not sure which contrast (F or T) I am supposed to use.
> > Is it correct to do a F test with the vector [-1 1] (cf. picture attached to
> > this mail) or do I have to complete for all the columns [-1 1 -1 1 -1 1...]
> > ?
> >
> > Any help would be more than appreciated!
> > Thank you very much in advance.
> >
> > Julie