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

[Arnaud Delorme]

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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