[FieldTrip] design matrix for ft_freqstatistics; between subjects

[liao ke]

Hi, Kathrin,

I meet similar question on comparison of ERP between two group subjects
using ft_timelockstatistics and  ft_timelockanalysis. One group has 12
subjects, another group has 43 subjects, and my design matrix is like

design = zeros(1, 55);
design(1, 1:12) = 1;
design(1, 12+1:end )= 2;
cfg.design = design;             % design matrix
cfg.ivar  = 1;


After I invoke ft_timelockanalysis, I use ft_timelockgrandaverage to
calculate grand average with cfg.keepindividual = 'yes' . Then the
following ft_timelockstatistics  works well. If I use cfg.keepindividual =
'no' in ft_timelockgrandaverage , the ft_timelockstatistics has error 'the
size of the design matrix does not match the number of observations in the
data'  in its statistics_wrapper subfunction.

My question is why I should keep all trials data (cfg.keepindividual =
'yes') in ft_timelockgrandaverage ? I guess the method in
ft_timelockstatistics should use subjects averaged data as sample ( average
over trials data of this subject ) not use all subjects trial-based data.
Am I correct?

Thanks for your help.

ke


On Sat, Dec 1, 2012 at 9:15 AM, Kathrin Müsch
<k.muesch at uke.uni-hamburg.de>wrote:

> Hi Nenad,
>
> It's like a between trials experiment within one subject (first example of
> the tutorial). Your design is correct. Remember to use independent samples
> statistics because you compare two independent groups (in your case
> subjects).
>
> cfg.statistic = 'indepsamplesT';
> cfg. design = design;
> cfg.ivar = 1;
>
> Best,
> Kathrin
>
> Am 01.12.2012 um 15:02 schrieb Nenad Polomac:
>
> > Hi everybody,
> >
> > I have some doubts concerning statistic in between subjects experiment.
> I couldn't find explanation for this case in tutorial.
> > I have two groups of subjects. And I would like to compare this two
> groups for the same condition using ft_freqstatistics (cfg.correctm =
> 'cluster'). I have two time frequency grand average for each group (8
> subjects in each group; cfg.keepindividual = 'yes';). I am not sure how a
> design matrix for ft_freqstatistics suppose to look like
> >
> > I suppose: design=[1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2]
> > Is this correct?
> >
> > Thank you in advance!
> >
> > Nenad
> >
> >
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