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<p class="MsoNormal"><span style="color:#1F497D">Dear Tobias,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Thank you for the hint! Indeed, this makes the calculation of the circular difference much easier and the resulting values stay between -pi and pi. Sorry that I didn’t think of this, since the purpose of the
function is rather obvious.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Best regards,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Thomas<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
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<b><span lang="DE" style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext">Von:</span></b><span lang="DE" style="font-size:10.0pt;font-family:"Tahoma","sans-serif";color:windowtext"> fieldtrip-bounces@science.ru.nl [mailto:fieldtrip-bounces@science.ru.nl]
<b>Im Auftrag von </b>Tobias Staudigl<br>
<b>Gesendet:</b> Mittwoch, 15. Januar 2014 10:19<br>
<b>An:</b> FieldTrip discussion list<br>
<b>Betreff:</b> Re: [FieldTrip] Problems with statistics for circular data<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Dear Thomas, <br>
<br>
try using circ_dist.m (in the circ_stats toolbox by Berens). <br>
This should solve the circular difference issue.<br>
<br>
all the best, <br>
Tobias<br>
<br>
Am 15.01.2014 09:35, schrieb <a href="mailto:Thomas.Baumgarten@med.uni-duesseldorf.de">
Thomas.Baumgarten@med.uni-duesseldorf.de</a>:<o:p></o:p></p>
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<p class="MsoNormal"><span lang="EN-GB" style="font-size:12.0pt;line-height:115%">Dear FieldTrip users,</span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:12.0pt;line-height:115%">I am working on a set of circular data (phase angles of ongoing oscillations computed via Hilbert transform) and would like to statistically compare two conditions (A,B). For
this, I use the circular statistics toolbox for matlab by P. Berens. I worked on this problem from two different angles:
</span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:12.0pt;line-height:115%">1. First, I tried to directly compare the two conditions via the Watson-Williams two-sample test (function: circ_wwtest). Unfortunately, this didn’t work out, since the test requires
an average resultant vector length of > 0.45 for n >= 11 entries/ subjects, an assumption which is not met by my data.</span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:12.0pt;line-height:115%">2. Second, I tried to calculate the angle of difference between the two conditions (angle(A) – angle(B)) and then used the one-sample mean angle test (function: circ_mtest) to
test if the resulting angle of difference is significantly different from zero. Here, the following problems arise: Since the resulting angles for A and B range from –pi to +pi, there are cases when the subtraction of the two angles results in roughly +2pi
or -2pi (e.g. cases where (A = pi) – (B = -pi) = 2pi), resulting in an error from the circ_mtest function. I tried to solve this problem by using a modulus (2pi) operation (i.e. by ‘cleaning out’ the redundant circumventions while at the same time preserving
the angle information), but unfortunately this didn’t work out either.</span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:12.0pt;line-height:115%">The only other option I can think of would be to generate surrogate data (i.e. a matrix with the same dimensions as the matrix with the angles of difference , only filled with
zeros) and to apply a cluster-based permutation test (similar to ft_freqstatitics). Although this would take care of my multiple-comparison problem, I am not quite sure if the cluster correction is still valid in this case and if this test would work for circular
data.</span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:12.0pt;line-height:115%">I would greatly appreciate any comments and advice on this matter.</span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:12.0pt;line-height:115%">Thanks for your help,</span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:12.0pt;line-height:115%">Thomas</span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:10.0pt;line-height:115%"> </span><o:p></o:p></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:10.0pt;line-height:115%"> </span><o:p></o:p></p>
<p class="MsoNormal" style="margin-bottom:0cm;margin-bottom:.0001pt"><span lang="EN-GB" style="font-size:9.0pt;line-height:115%">Thomas Baumgarten, PhD Student</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-bottom:0cm;margin-bottom:.0001pt"><span lang="EN-GB" style="font-size:9.0pt;line-height:115%">Institute of Clinical Neuroscience and Medical Psychology, Medical Faculty, Heinrich-Heine-University Düsseldorf, Universitätsstraße
1, 40225 Düsseldorf, Germany</span><o:p></o:p></p>
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<span style="font-size:12.0pt;font-family:"Times New Roman","serif""><br>
<br>
<br>
<o:p></o:p></span></p>
<pre>_______________________________________________<o:p></o:p></pre>
<pre>fieldtrip mailing list<o:p></o:p></pre>
<pre><a href="mailto:fieldtrip@donders.ru.nl">fieldtrip@donders.ru.nl</a><o:p></o:p></pre>
<pre><a href="http://mailman.science.ru.nl/mailman/listinfo/fieldtrip">http://mailman.science.ru.nl/mailman/listinfo/fieldtrip</a><o:p></o:p></pre>
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<span style="font-size:12.0pt;font-family:"Times New Roman","serif""><br>
<br>
<br>
<o:p></o:p></span></p>
<pre>-- <o:p></o:p></pre>
<pre>Dr. Tobias Staudigl<o:p></o:p></pre>
<pre>Fachbereich Psychologie - ZPR<o:p></o:p></pre>
<pre>Postfach ZPR<o:p></o:p></pre>
<pre>78457 Konstanz<o:p></o:p></pre>
<pre>ZPR, Haus 12<o:p></o:p></pre>
<pre>Tel.: +49 (0)7531 / 88 - 5703<o:p></o:p></pre>
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