Dear Zoi,
Fit of DCM model to the data and percentage of variance in the
original data explained by the modes are two unrelated issues. Yes, to
show that the fit is fair the display in 'Resuts' is OK and to compare
between different models you should use the model evidence (BMS
button) which integrates model fit and model complexity.
Best,
Vladimir
On Thu, Nov 19, 2009 at 4:22 PM, Zoi Da <[log in to unmask]> wrote:
> Dear Vladimir,
>
> Thanks a lot for your answer.
>
> I just want to understand what exactly this 'Now the spatial modes are based
> on the leadfields of the
> sources included in DCM models rather than on the data.' means. Does this
> have any implications about the results? If for example I have to justify
> that the proposed model that I have created fits my data, is the model fit
> given in SPM8 as -ERPs (mode)- sufficient?
>
> Again thanks for your time.
>
> Best
>
> Zoi
>
> ________________________________
> Von: Vladimir Litvak <[log in to unmask]>
> An: Zoi Da <[log in to unmask]>
> CC: SPM@jiscmail.ac..uk
> Gesendet: Donnerstag, den 19. November 2009, 16:03:21 Uhr
> Betreff: Re: [SPM] WG: DCM_EEG
>
> Dear Zoe,
>
> I briefly looked at the code and it seems that what it does now is not
> exactly the same as what was done when those papers were being
> prepared. Now the spatial modes are based on the leadfields of the
> sources included in DCM models rather than on the data. So there is no
> place in the code where the percentage of data variance explained by
> these modes is computed. This could possibly be done with some custom
> code but writing such code would require some expertise.
>
> Best,
>
> Vladimir
>
> On Thu, Nov 19, 2009 at 3:50 PM, Zoi Da <[log in to unmask]> wrote:
>> Dear Vladimir,
>>
>> My mistake for not explaining.
>>
>> In various articles of Garrido et al. (2007;2008;2009), they state that
>> 'the use of three principal eigenvariates (spatial modes) preserved more
>> than 73% of the variance in all subjects.' I was wondering how someone can
>> test that? I have used 8 spatial modes, how can i test how much variance
>> they explain in al subjects? Where are these values stored?
>>
>> Hope that it is clearer now!
>>
>> Best
>>
>> Zoi
>>
>> P.S. Thanks for taking the time
>>
>> ________________________________
>> Von: Vladimir Litvak <[log in to unmask]>
>> An: Zoi Da <[log in to unmask]>
>> CC: SPM@jiscmail.ac..uk
>> Gesendet: Donnerstag, den 19. November 2009, 15:23:17 Uhr
>> Betreff: Re: [SPM] WG: DCM_EEG
>>
>> Dear Zoi,
>>
>> It's not quite clear to me what you want to do. Perhaps you could
>> describe the aim of your analysis and then it's be easier to help you.
>>
>> Best,
>>
>> Vladimir
>>
>> 2009/11/19 Zoi Da <[log in to unmask]>:
>>>
>>>
>>> ----- Weitergeleitete Mail ----
>>> Von: Zoi Da <[log in to unmask]>
>>> An: [log in to unmask]
>>> Gesendet: Donnerstag, den 19. November 2009, 14:56:12 Uhr
>>> Betreff: DCM_EEG
>>>
>>> Hi everyone
>>>
>>> My name is Zoi and I have been analyzing EEG data with DCM. I have
>>> computed
>>> the DCMs to eight spatial modes. I would like know how I can compute the
>>> variance of the data?
>>>
>>> Thanks a lot
>>>
>>>
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