[Mne_analysis] Unbalanced number of trials between individuals: problem in sources

Denis-Alexander Engemann denis.engemann at gmail.com
Thu Mar 3 10:43:08 EST 2016
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Yes that's the idea. Amplitudes of the inverse solution are scaled by the
number of trials (.nave). This should work as an heuristic unless you
compare rare to frequent events (e.g. oddball).
Hope this helps.

On Thu, Mar 3, 2016 at 4:38 PM, Laetitia Grabot <laetitia.grabot at gmail.com>
wrote:

> So does that mean that we need not to equalize epochs between conditions
> (within one subject)?
>
> 2016-03-03 16:23 GMT+01:00 Denis-Alexander Engemann <
> denis.engemann at gmail.com>:
>
>> Hi Laetitia,
>>
>> I I'm understanding you correctly this should not be an issue for evoked
>> data as long as you are using the .average method that will tell the
>> inverse routines how to scale the data via its .nave attribute.
>> Did you have any particular problems?
>>
>> Cheers,
>> Denis
>>
>> On Thu, Mar 3, 2016 at 3:09 PM, Laetitia Grabot <
>> laetitia.grabot at gmail.com> wrote:
>>
>>> Dear MNE-users,
>>>
>>> I am aware of the fact that when contrasting two conditions, the epochs
>>> within each condition should be equalized before reconstructing in source
>>> space, otherwise the SNR would be different between the two conditions.
>>> That also means that if two subjects have a different number of epochs, the
>>> SNR of each subject will be different. It is often the case that the number
>>> of epochs doubled between subjects (50 vs. 100) so I guess that it is an
>>> issue when looking at group averaged stc for instance.
>>> A possible solution would be to normalize the stc to correct for the
>>> number of trials. What do you think of that? What would be the proper
>>> normalization?
>>>
>>> Thanks,
>>> Best,
>>> Laetitia G.
>>>
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