David Field wrote:
> Dear SPMers,
>
> I have conducted conjunction analysis on individual subject data, and wish
> to replicate it as a random effects analysis at the 2nd level.
>
> Previously, I have had a simple 1 -1 t contrast at the single subject level.
> To perform 2nd level analysis I chose the 1 sample t test option from "Basic
> Models", and specified the con files associated with the 1 -1 contrast from
> each subject.
>
> In the case of a conjunction analysis, SPM2 does not produce a con file for
> the contrast; instead it uses the two existing con files chosen for
> conjunction to produce an SPM. Therefore, there is no con file for me to
> select at the second level using the 1 sample to test option.
>
> I have an idea how to do the conjunction analysis at the 2nd level, but am
> not sure if it is correct. I think I should select the "one way anova"
> option (not the anova with constant or within subjects anova), and specify 2
> groups. For the 1st group I should select the con files for the first
> contrast that is part of my conjunction analysis, and for the 2nd group I
> should specify the 2nd contrast that is part of the conjunction.
>
> Once I've estimated the model, I should specify contrasts for each of my
> groups (1 0 and 0 1). Then, I can select both contrasts together using ctrl+
> click in order to perform the conjunction analysis at the 2nd level.
>
> I'd be very happy if someone could tell me that my idea of how to do this
> analysis is correct, or if not, how I should do it.
>
Yes. That's the correct way to do it.
> I have a second question about carrying F contrasts to the 2nd level. Each F
> contrast I perform for an individual subject creates an "ess" file. Are
> these "ess" files used at the 2nd level instead of the "con" images created
> by t contrasts?
>
No. The con images are used at the second level. See eg. the note ANOVAS and SPM
available from:
http://www.fil.ion.ucl.ac.uk/~wpenny/publications/rik_anova.pdf
Best wishes,
Will.
> Thanks,
> David Field
>
> ---------------------------------
>
> Dr David Field
> Department of Psychology
> Room 1S20
> Earley Gate
> University of Reading
> RG6 6AL
>
> +44 (0)118 3785004
>
> ---------------------------------
>
>
>
--
William D. Penny
Wellcome Department of Imaging Neuroscience
University College London
12 Queen Square
London WC1N 3BG
Tel: 020 7833 7478
FAX: 020 7813 1420
Email: [log in to unmask]
URL: http://www.fil.ion.ucl.ac.uk/~wpenny/
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