Dear Neil,
for a paired T-test, you should set "Variance" to "Equal" when
specifying your model.
And be careful of the interpretation of the results of a 'preliminary
analysis' with few degrees of freedom....
Best regards,
Guillaume.
Neil Chatterjee wrote:
> Dear SPMers,
>
> I've stumbled into a problem I can't seem to figure out. I set up a paired
> t-test with 8 individuals (small N, I know, but this is only a preliminary
> analysis). After model specification, everything looked fine. There are 10
> "conditions" just as expected. But after estimating the model the design
> matrix vanishes (the graph is completely white). 10 beta maps are written
> out, but when I open up the SPM.mat to look at results, there is no visible
> design matrix, and I'm told the contrast vectors I'm specifying are not
> valid. When the contrast manager launches, MATLAB gives me the following error:
>
>
> SPM5: spm_results_ui (v$Rev: 1776 $) 15:45:33 - 18/05/2009
> ========================================================================
> ??? Error using ==> image
> Error using ==> image
> Image CData can not be complex
>
> Error in ==> spm_conman at 975
> hDesMtxIm = image((varargin{2}.nKX+1)*32);
>
> Error in ==> spm_conman at 944
> spm_conman('ImDesMtx',xX,H.hDesMtxAx) %-Depict
> DesMtx
>
> Error in ==> spm_conman at 812
> [F,cF] =
> spm_conman('Initialise','on',SPM,STATmode,n,Prompt,Mcstr,OK2chg);
>
> Error in ==> spm_getSPM at 248
> [Ic,xCon] = spm_conman(SPM,'T&F',Inf,...
>
> Error in ==> spm_results_ui at 274
> [SPM,xSPM] = spm_getSPM;
>
> ??? Error while evaluating uicontrol Callback
>
>
> Anybody know what's happening? I've attached the job script for specifying
> the model. I am using SPM5 in Matlab R2008b.
>
> Regards,
> Neil
>
> Neil Chatterjee
> Stanford Systems Neuroscience and Pain Lab
> [log in to unmask]
--
Guillaume Flandin, PhD
Wellcome Trust Centre for Neuroimaging
University College London
12 Queen Square
London WC1N 3BG
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