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

Laetitia Grabot laetitia.grabot at gmail.com
Thu Mar 3 11:15:09 EST 2016
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Ok good to know, thanks!

2016-03-03 17:07 GMT+01:00 Denis-Alexander Engemann <
denis.engemann at gmail.com>:

> I think there is actually no strong reason for that. Maybe some
> unintentionally copied line.
>
> On Thu, Mar 3, 2016 at 5:02 PM, Laetitia Grabot <laetitia.grabot at gmail.com
> > wrote:
>
>> Ok, thanks, I was still applying the old advice of equalizing epochs
>> between conditions! But so, why in certain statistical examples of the
>> website, you're still equalizing conditions (like in the Reapeated-measures
>> ANOVA in sources)?
>>
>> 2016-03-03 16:43 GMT+01:00 Denis-Alexander Engemann <
>> denis.engemann at gmail.com>:
>>
>>> 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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