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<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>Dear all, <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>I have a question concerning cluster based
permutation statistics.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>It is more a basic question on the difference between
one- and two-sided testings. I recall from simple t-tests that as an approach
to your two-sided p-value you can multiply your one-sided p-value by 2. I hope
this is correct? And I am assuming this to also hold in the other direction,
thus, approximating your one-sided p-value by dividing your two-sided p-value by
2?<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>That is why I am expecting something similar when
calculating my statistics with a cluster based permutation approach.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>So what I am actually doing is comparing two
conditions at one sensor, comparing time-frequency data. <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>When I calculate a two-sided dependent samples t-test
<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>(cfg = [];<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>cfg.channel =
'all';
<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>cfg.latency = [0.5
1.5];
<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>cfg.avgoverchan = 'no';<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>cfg.avgovertime = 'no';<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>cfg.parameter =
'powspctrm';
<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>cfg.method = 'montecarlo';
<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>cfg.statistic = 'depsamplesT';<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>cfg.correctm = 'cluster';<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>cfg.clusteralpha = 0.05;<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>cfg.clusterstatistic =
'maxsum';
<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>cfg.tail =
0;
<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>cfg.clustertail =
0;
<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>cfg.alpha = 0.025;<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>cfg.numrandomization = 1000; <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>)<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>, I find one positive cluster with a p-value of
0.036, thus not significant (see fig 1).<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-GB style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>When I then change my settings to a one-sided test<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=FR style='font-size:10.0pt;
font-family:Arial'>(cfg.tail = 1;
<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=FR style='font-size:10.0pt;
font-family:Arial'>cfg.clustertail =
1;
<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=FR style='font-size:10.0pt;
font-family:Arial'>cfg.alpha = 0.05;)<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>, the positive cluster gets a p-value of 0.056, again
not significant (see fig 2). <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>With the assumption described above, however, I would
expect this to become significant when using a one-sided test. Is my assumption
correct? If not, could anybody comment on what is wrong about my assumption?<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>I would be very grateful for any advice!<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>Kind regards and thank you very much in advance! <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'>Nina<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span lang=EN-US style='font-size:
10.0pt;font-family:Arial'><o:p> </o:p></span></font></p>
<p class=FormatvorlageArial10ptVor5ptNach5pt><font size=2 face=Arial><span
lang=EN-GB style='font-size:10.0pt'>- - - - - - - - - - - - - - - - - - - - - -
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -<o:p></o:p></span></font></p>
<p class=FormatvorlageArial10ptVor5ptNach5pt><font size=2 face=Arial><span
lang=EN-GB style='font-size:10.0pt'><o:p> </o:p></span></font></p>
<p class=FormatvorlageArial10ptVor5ptNach5pt><font size=2 face=Arial><span
lang=EN-GB style='font-size:10.0pt'>Nina Kahlbrock<o:p></o:p></span></font></p>
<p class=FormatvorlageArial10ptVor5ptNach5pt><font size=2 face=Arial><span
lang=EN-GB style='font-size:10.0pt'>Institute of Clinical Neuroscience and
Medical Psychology <o:p></o:p></span></font></p>
<p class=FormatvorlageArial10ptVor5ptNach5pt><font size=2 face=Arial><span
style='font-size:10.0pt'>Heinrich Heine University Duesseldorf<o:p></o:p></span></font></p>
<p class=FormatvorlageArial10ptVor5ptNach5pt><font size=2 face=Arial><span
style='font-size:10.0pt'>Universitaetsstr. 1<o:p></o:p></span></font></p>
<p class=FormatvorlageArial10ptVor5ptNach5pt><font size=2 face=Arial><span
style='font-size:10.0pt'>40225 Düsseldorf<o:p></o:p></span></font></p>
<p class=FormatvorlageArial10ptVor5ptNach5pt><font size=2 face=Arial><span
style='font-size:10.0pt'><o:p> </o:p></span></font></p>
<p class=FormatvorlageArial10ptVor5ptNach5pt><font size=2 face=Arial><span
style='font-size:10.0pt'>Tel.: +49 211 81 18075<o:p></o:p></span></font></p>
<p class=FormatvorlageArial10ptVor5ptNach5pt><font size=2 face=Arial><span
style='font-size:10.0pt'>Fax. .: +49 211 81 19916<o:p></o:p></span></font></p>
<p class=FormatvorlageArial10ptVor5ptNach5pt><font size=2 face=Arial><span
style='font-size:10.0pt'><o:p> </o:p></span></font></p>
<p class=FormatvorlageArial10ptVor5ptNach5pt><font size=2 face=Arial><span
style='font-size:10.0pt'>Mail: </span></font><span lang=FR><a
href="mailto:Nina.Kahlbrock@med.uni-duesseldorf.de"><font color=black><span
lang=DE style='color:windowtext;text-decoration:none'>Nina.Kahlbrock@med.uni-duesseldorf.de</span></font></a></span><o:p></o:p></p>
<p class=FormatvorlageArial10ptVor5ptNach5pt><font size=2 face=Arial><span
lang=FR style='font-size:10.0pt'><a
href="http://www.uniklinik-duesseldorf.de/medpsychologie"><font color=black><span
lang=DE style='color:windowtext;text-decoration:none'>http://www.uniklinik-duesseldorf.de/medpsychologie</span></font></a></span><o:p></o:p></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
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