[Eeglablist] Is power calculated in STUDY and in dataset is abs or relative?

[Arnaud Delorme]

Dear Aleksandra,

there is a check box in the STUDY menu that allows you to subtract the average power from each individual. Does that solve your problem?
Thanks,

Arno

On 11 Oct 2012, at 23:39, Aleksandra Vuckovic wrote:

> Dear Arno,
> that is what I've expected but how can one then compare powers between two group ( looking at a peak frequency of e.g. two groups of patients) being sure that the difference does not come from individual difference in EEG amplitude?
> Or other way around, how can we replace a value of the absolute power in a STUDY with the relative power and then visualise it using the STUDY tools?
> Many thanks,
> Aleksandra
>  
> From: Arnaud Delorme [arno at ucsd.edu]
> Sent: 12 October 2012 02:28
> To: Aleksandra Vuckovic
> Cc: tarikbelbahar at gmail.com; M Abul Hassan; eeglablist at sccn.ucsd.edu
> Subject: Re: [Eeglablist] Is power calculated in STUDY and in dataset is abs or relative?
> 
> Dear Aleksandra,
> 
> power is absolute when plotting the spectrum and relative to baseline when computing ERSP as Tarik mentioned.
> Best,
> 
> Arno
> 
> On 9 Oct 2012, at 01:48, Aleksandra Vuckovic wrote:
> 
>> Hi,
>> what Abul Hasan is asking is whether the Power calculated in EEGLab in certain frequency band is absolute or relative (e.g. for example is it Power (8-12 Hz) or Power (8-12 Hz)/Power(1-40 Hz) )
>> This is a relevant question if one wants to compare mean Power values between two groups in a STUDY. We need to be sure that the difference is not coming from the fact that people in one group have a higher amplitude EEG  but that their relative power in certain frequency band is higher as compare  to the other group.
>> Can anybody give us a clue how to get a relative power using STUDY so we can use all nice graphical presentation and statistics?
>>  
>> Many thanks,
>> Aleksandra
>>  
>> From: eeglablist-bounces at sccn.ucsd.edu [eeglablist-bounces at sccn.ucsd.edu] On Behalf Of Tarik S Bel-Bahar [tarikbelbahar at gmail.com]
>> Sent: 08 October 2012 22:41
>> To: M Abul Hassan
>> Cc: eeglablist at sccn.ucsd.edu
>> Subject: Re: [Eeglablist] Is power calculated in STUDY and in dataset is abs or relative?
>> 
>> Greetings Abdul,
>> 
>> I am not an expert on the mechanics here,
>> but I believe if you are referring to ERSP computation using the newtimef function,
>> then the baseline of values before the 0 time point in your epochs is automatically subtracted.
>> Please also see  multiple messages on this topic in recent months in the eeglablist archives.
>> 
>> Respectfully,
>> Tarik
>> 
>> 
>> 
>> 
>> 
>> On Fri, Oct 5, 2012 at 2:37 AM, M Abul Hassan <abulhassan85 at yahoo.com> wrote:
>> Dear all
>>  
>> I want to know the power spectrum generated by EEGLAB both in a STUDY and in each dataset seperately is using absolute values or relative values.
>>  
>> If it based on relative values than how a frequency range can be known?
>>  
>> If it is based on absolute values than how can I calculate the relative power in EEGLAB?
>>  
>> Thanks
>> Best Regards
>> Muhammad Abul Hasan
>> 
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