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<font size="2" face="Arial,Helvetica,sans-serif"><span style="font-size:10pt;"><font color="black" face="Helvetica"><span dir="ltr">Hi Laetitia,<br>
<br>
If you only have one subject you do need individual trial data, otherwise you can't do statistics like this.<br>
You need multiple observations (either subjects or trials).<br>
<br>
Best,<br>
Tineke<br>
<br>
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<div style="direction: ltr;" id="divRpF533353"><font color="#000000" size="2" face="Tahoma"><b>From:</b> fieldtrip-bounces@science.ru.nl [fieldtrip-bounces@science.ru.nl] on behalf of laetitia.lalla@inserm.fr [laetitia.lalla@inserm.fr]<br>
<b>Sent:</b> Thursday, March 31, 2016 1:11 PM<br>
<b>To:</b> fieldtrip@science.ru.nl<br>
<b>Subject:</b> [FieldTrip] Question about coherence statistics<br>
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<p style="margin-bottom:0in; line-height:100%">Dear FielTrip community,</p>
<p style="margin-bottom:0in; line-height:100%">Sorry to bother you again...</p>
<p style="margin-bottom:0in; line-height:100%">I have a question about the statistical testing to assess coherence differences and the related paper by E Maris, JM Schoffelen and P Fries (Journal of Neuroscience Methods, 2007)</p>
<p style="margin-bottom:0in; line-height:100%">I believe I am exactly in the framework described in this paper, but I guess there is still some crucial information that I don't understand...</p>
<p style="margin-bottom:0in; line-height:100%"> </p>
<p style="margin-bottom:0in; line-height:100%">This is my story :</p>
<p style="margin-bottom:0in; line-height:100%">- It's a single-subject study</p>
<p style="margin-bottom:0in; line-height:100%">- I want to compare two sets of trials observed in different conditions.</p>
<p style="margin-bottom:0in; line-height:100%">- The 2 sets of trials are exactly the same size, so my coherence estimate won't be biased by the $B!H(Bunequal sample size problem$B!I(B.</p>
<p style="margin-bottom:0in; line-height:100%">- I just want to compare for 1 channel pair, for 1 frequency bin [6Hz 10Hz], so I guess the Multiple Comparison problem won't affect my analysis too much (either in the spatial or the spectral dimension).</p>
<p style="margin-bottom:0in; line-height:100%"> </p>
<p style="margin-bottom:0in; line-height:100%">Based on the paper, I could refer myself to the point $B!H(B2.7.1. A non parametric satistical test for a single signal pair and a single frequency bin$B!I(B.</p>
<p style="margin-bottom:0in; line-height:100%">- Since my interest is in the coherence difference for a single signal pair, I can choose [|C1(f)|-|C2(f)|] as a test statistic.</p>
<p style="margin-bottom:0in; line-height:100%">- And I can perform the montecarlo simulation.</p>
<p style="margin-bottom:0in; line-height:100%"> </p>
<p style="margin-bottom:0in; line-height:100%">My question is the following : How can I implement the nonparametric test of the coherence difference between my 2 conditions with the fieldtrip functions ?</p>
<p style="margin-bottom:0in; line-height:100%"> </p>
<p style="margin-bottom:0in; line-height:100%">This is what I did :</p>
<p style="margin-bottom:0in; line-height:100%">1) Extract and preprocess the signal from my condition 1.</p>
<p style="margin-bottom:0in; line-height:100%">2) freq1= ft_freqanalysis(cfg, signal1) (with cfg.method='mtmfft', cfg.output='powandcsd') $B"*(B</p>
<p style="margin-bottom:0in; line-height:100%">3) coh1= ft_connectivityanalysis(cfg, freq1)</p>
<p style="margin-bottom:0in; line-height:100%"> </p>
<p style="margin-bottom:0in; line-height:100%">I did the same thing for the other condition $B"*(B coh2.</p>
<p style="margin-bottom:0in; line-height:100%"> </p>
<p style="margin-bottom:0in; line-height:100%">And then for the statistics :</p>
<p style="margin-bottom:0in; line-height:100%">cfg = [];</p>
<p style="margin-bottom:0in; line-height:100%">cfg.statistic = 'diff'; (% because the statistic test than I chose is the difference [|C1(f)|-|C2(f)|])</p>
<p style="margin-bottom:0in; line-height:100%">cfg.parameter='cohspctrm';</p>
<p style="margin-bottom:0in; line-height:100%">cfg.method = 'montecarlo';</p>
<p style="margin-bottom:0in; line-height:100%">cfg.numrandomization = 1000;</p>
<p style="margin-bottom:0in; line-height:100%">cfg.ivar = 1;</p>
<p style="margin-bottom:0in; line-height:100%">cfg.alpha=0.05;</p>
<p style="margin-bottom:0in; line-height:100%">cfg.tail=0;</p>
<p style="margin-bottom:0in; line-height:100%">cfg.correcttail='alpha';</p>
<p style="margin-bottom:0in; line-height:100%">stat=ft_freqstatistics(cfg, coh1, coh2);</p>
<p style="margin-bottom:0in; line-height:100%"> </p>
<p style="margin-bottom:0in; line-height:100%">And it gives me the following error :</p>
<p style="margin-bottom:0in; line-height:100%">Error using ft_checkconfig (line 153)</p>
<p style="margin-bottom:0in; line-height:100%">The field cfg.design is required.</p>
<p style="margin-bottom:0in; line-height:100%"> </p>
<p style="margin-bottom:0in; line-height:100%">Here, I really don't understand why I'm asked for the design matrix... When doing the statistics for the Power, I understood that the design matrix was telling which trial belonged to the condition 1 and which
trial belonged to the condition 2. But here, it doesn't make any sense because my coherence was calculated by averaging on the trials...</p>
<p style="margin-bottom:0in; line-height:100%">Does the design matrix mean something differently here ? Or maybe I forgot one parameter to put in the cfg ?</p>
<p style="margin-bottom:0in; line-height:100%"> </p>
<p style="margin-bottom:0in; line-height:100%">Any help will be appreciated !</p>
<p style="margin-bottom:0in; line-height:100%"> </p>
<p style="margin-bottom:0in; line-height:100%">Thanks a lot for your time,</p>
<p style="margin-bottom:0in; line-height:100%"> </p>
<p style="margin-bottom:0in; line-height:100%">Laetitia Lalla</p>
<p style="margin-bottom:0in; line-height:100%">PhD student in Neurosciences</p>
<p style="margin-bottom:0in; line-height:100%">INMED, Marseille, France</p>
<p style="margin-bottom:0in; line-height:100%"> </p>
<p style="margin-bottom:0in; line-height:100%"> </p>
<p> </p>
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