Dear Dudley,
In this instance, you should set 'Variance' to be 'Equal' in your
two-sample T-test.
Best regards,
Guillaume.
Dudley Ibbett wrote:
> Hi
>
> I am trying to set up a simple SPM unpaired T test comparing a single
> patients TcHMPAO SPECT data set with a 20 controls (studies that have
> been reported as "normal"). I am using SPM8b with the following basic
> model parameters: Two Sample T-test, Threshold Masking: Relative, Global
> Calculation: Mean, Global Normalistation: Yes, Normalisation: Proportional.
>
> I have found an article on the web by Rik Henson (MRC) on this subject
> and the Two-Sample T-test appears to be recommended. This articles
> suggests I should be able to use the T-contrast [1 -1] to test the
> control group against the single patient, however SPM tells me this is
> and invalid contrast. The only contrast it allows is [0 1]. I would be
> very grateful if someone could explain what I am doing wrong.
> Presumably I should be able to set up a contrast that will test
> for areas where the single patient is greater that the control group and
> also a contrast that test for areas where the single patient is less
> than the control group.
>
> Many Thanks
>
> Dudley
--
Guillaume Flandin, PhD
Wellcome Trust Centre for Neuroimaging
University College London
12 Queen Square
London WC1N 3BG
|