[FieldTrip] scaling frequency data for comparison

[jakob kaiser]

Dear list,I wanted to compare the outputs from different ft_freqanalysis-methods to see if they make significant differences in the final test results of my data. This were the parameters used:

cfg.output       = 'pow';cfg.channel      = 'all';cfg.method       = 'mtmconvol';cfg.taper        = 'hanning';cfg.foi          = 6:2:20;                    cfg.t_ftimwin    = ones(length(cfg.foi),1).*0.5;   cfg.toi          = -0.5:0.05:2; 

WaveletConfig.method = 'wavelet'; WaveletConfig.output = 'pow'; WaveletConfig.foi = 6:2:20; WaveletConfig.toi = -0.5:0.05:2;
(I chose these two methods because I found them used un papers relevant for my work)Now, as has been discussed on the list before, the scaling of the output data is very different. While the mtconvol-hanning-method gives me data points between roughly -2 an 1, with the wavelet-method I have data between roughly -800 and 600. From the (btw very helpful) tutorials and the previous list discussions I understand that this is a normal byproduct of the mathematical methods employed. However, for comparing different outputs it would be useful to scale both produced data sets to the same unit, so to speak. As both methods are supposed to measure the same thing, it should someone be possible to scale them to similar sizes, shouldn't it? Is there such a way? (Ultimately, I will have to compare the data results to results from a completely different program, which seem to have a third, different scaling altogether, so I am really puzzled how to handle the differences in scale)Generally, although this has been mentioned before, I am still not sure, if it is possible to put a certain unit to the results. Power is often reported in mV^2/Hz. If my initial data is in mV, would it be correct to say, that the hanning-method describe above delivers data in mV^2/Hz? Would this be correct for the Wavelet-method? Obviously, both cannot be true, because the scaling is extremely different. So, is it possible to specify a unit for any of these methods? Is there a way to convert the output   of ft_freqanalysis-methods to this or another meaningful unit?I would be very grateful, if someone could give me a hint, how to interpret the data points here.Thank you for reading + thanks to the programmers for fieldtrip, which I like a lot
Jakob 		 	   		  
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.science.ru.nl/pipermail/fieldtrip/attachments/20110816/e9fee596/attachment-0001.html>