Jigar Jogia wrote:
>
> Hi Will
>
> Had a couple of questions for you, I am trying to do a simple case control
> comparison between 21 patients and 21 controls.
> I tried to use "Two sample t-test" in "Basic models".
> For "Source images" I selected 21 control images and then the 21 patient
> images.
> For "set up analysis" I typed "cx21 and px21
> I input all "no" to "grand mean scaling", "Threshold masking",
> "threshold", "Implicit mask", "explicitly mask", "Global calculation",
> "non-sphericity correction". Then I clicked "estimate". After calculation
> I clicked "Results".
> In SPM contrast manager, I selected "Define new contrast". I entered
> "control>patient" for name,
> "t-contrast for type" and "1 -1" for contrast.
>
> 1.) I think the above step are comparing the patients with the controls and
> giving the differences, is that correct?
Yes.
> 2.) Is this okay? and what should i do for the next steps? (After entering
> the contrast)
Yes this is OK. Look at the SPM for this effect with FWE p<0.05 to see if there
are any consistent differences between groups.
> 3.) Is there anything else I can try ?
Yes. Some areas may show greater response for patients than controls. YOu can
test this with the t-contrast [-1 1]. Or use an F-contrast [1 -1] to test for
both at the same time.
Best,
Will.
>
> Thanking you in advance
>
> Best wishes
>
> Jigz
>
>
> ----------------------------------------------------------------------
> Mr. Jigar Jogia
> Research Worker
> Section of Neurobiology of Psychosis
> Division of Psychological Medicine
> P066 Institute of Psychiatry
> De Crespigny Park
> London SE5 8AF
> United Kingdom
>
> Tel: 0207 848 0611 / 07970 982 747
> Fax: 02078480657
> E-mail: [log in to unmask]
> ----------------------------------------------------------------------
>
>
>
>
--
William D. Penny
Wellcome Department of Imaging Neuroscience
University College London
12 Queen Square
London WC1N 3BG
Tel: 020 7833 7475
FAX: 020 7813 1420
Email: [log in to unmask]
URL: http://www.fil.ion.ucl.ac.uk/~wpenny/
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