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<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">Dear Jose,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">If you assume there to be (perhaps trivial) differences in the baselines of conditions A and B, but you are interested in the difference in change from baseline then doing
a baseline correction is indeed what you want to do. If you do not assume a difference at baseline it is in principle not necessary to correct for it (It might even hurt:
<a href="http://datacolada.org/39">http://datacolada.org/39</a>) .<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">With regards to ‘demeaning’ (and detrending), have a look at these two pages:
<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"><a href="http://www.fieldtriptoolbox.org/faq/why_does_my_tfr_look_strange">http://www.fieldtriptoolbox.org/faq/why_does_my_tfr_look_strange</a><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"><a href="http://www.fieldtriptoolbox.org/faq/why_does_my_tfr_look_strange_part_ii">http://www.fieldtriptoolbox.org/faq/why_does_my_tfr_look_strange_part_ii</a><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">It might be beneficial to demean and detrend before doing your frequency analysis.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">Best,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">Jim<o:p></o:p></span></p>
<p class="MsoNormal"><b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span style="font-size:11.0pt;font-family:"Calibri",sans-serif"> fieldtrip-bounces@science.ru.nl [mailto:fieldtrip-bounces@science.ru.nl]
<b>On Behalf Of </b>Jose<br>
<b>Sent:</b> Monday, July 18, 2016 6:08 PM<br>
<b>To:</b> fieldtrip@science.ru.nl<br>
<b>Subject:</b> [FieldTrip] cluster-based permutation test - baseline correction<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt">dear community,<br>
<br>
I'm performing analysis of CTF MEG data. I have two conditions of interest: A and B, and I have performed spectral decomposition with the wavelet method to obtain the power (frequencies from 1 to 50 Hz). I would like to perform a cluster-based permutation test
to assess if there are significant power differences between my two conditions of interest between the onset of my stimulus and 1 sec after,<br>
<br>
While I understand the principles of cluster-based permutation test, with their distinct versions: between trials, within trials and within subjects, what I am interested in is to test differences between my two conditions in their baseline-corrected versions.
Since I haven't seen this procedure in the tutorial, but it seems logic to me, I would like to verify the way to proceed is do baseline correction (for each condition and subject) and then run my cluster-permutation test. Is there anything else I should consider?<br>
<br>
Also, since I haven't used 'demean' during my trial definition (I was advised not to do this), I was wondering if this could impact my baseline correction, and subsequent statistical analysis. I've seen some messages in the forum referring to this procedure,<br>
<br>
Thanks in advance,<o:p></o:p></p>
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<p class="MsoNormal">Jose<o:p></o:p></p>
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