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<p class="MsoNormal">Dear group,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I do face some weird results during my analysis.<o:p></o:p></p>
<p class="MsoNormal">Usually I do t-test analysis to compare 2 condions/groups and use 2-tails, as far as I do not have any preliminary hypothesis about the direction of the effect.<o:p></o:p></p>
<p class="MsoNormal" style="text-autospace:none">So my script looks something like Script 1 (see below). Important here is that I do keep the default parameters,
<span style="font-size:12.0pt;font-family:"Courier New";color:black">cfg.tail = 0; cfg.clustertail = 0;</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal">To my understanding of statistic, if you have the two-tail effect, and group 1 has bigger mean than gr2, you should have the effect with one-tail as well and even more significant. But what I discovered just today that if I change this
parameter to 1, <span style="font-size:12.0pt;font-family:"Courier New";color:black">
cfg.tail = 1; cfg.clustertail = 1; in order to look spesifically for the one-tail effect (gr1 is bigger than gr2), my very significant 2 tail effect just disappeared completely. Is it a bug?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Courier New";color:black"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Courier New";color:black">Your comments are appreciated.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Courier New";color:black">Best reGards,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Courier New";color:black">Olga.</span><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Script 1<o:p></o:p></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:12.0pt;font-family:"Courier New";color:black">cfg = [];</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:12.0pt;font-family:"Courier New";color:black">cfg.method =
</span><span style="font-size:12.0pt;font-family:"Courier New";color:#A020F0">'montecarlo'</span><span style="font-size:12.0pt;font-family:"Courier New";color:black">;
</span><span style="font-size:12.0pt;font-family:"Courier New";color:forestgreen">% use the Monte Carlo Method to calculate the significance probability</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:12.0pt;font-family:"Courier New";color:black">cfg.statistic =
</span><span style="font-size:12.0pt;font-family:"Courier New";color:#A020F0">'indepsamplesT'</span><span style="font-size:12.0pt;font-family:"Courier New";color:black">;
</span><span style="font-size:12.0pt;font-family:"Courier New";color:forestgreen">% use the independent samples T-statistic as a measure to evaluate
</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:12.0pt;font-family:"Courier New";color:black"> </span><span style="font-size:12.0pt;font-family:"Courier New";color:forestgreen">% the effect at the sample
level</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:12.0pt;font-family:"Courier New";color:forestgreen">% cfg.statistic = 'indepsamplesF'; % use the independent samples T-statistic as a measure to evaluate
</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:12.0pt;font-family:"Courier New";color:forestgreen">% cfg.computecritval = 'yes' % the effect at the sample level</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:12.0pt;font-family:"Courier New";color:black">cfg.correctm =
</span><span style="font-size:12.0pt;font-family:"Courier New";color:#A020F0">'cluster'</span><span style="font-size:12.0pt;font-family:"Courier New";color:black">;</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:12.0pt;font-family:"Courier New";color:black">cfg.clusteralpha = 0.05;
</span><span style="font-size:12.0pt;font-family:"Courier New";color:forestgreen">% alpha level of the sample-specific test statistic that will be used for thresholding</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:12.0pt;font-family:"Courier New";color:black">cfg.clusterstatistic =
</span><span style="font-size:12.0pt;font-family:"Courier New";color:#A020F0">'maxsum'</span><span style="font-size:12.0pt;font-family:"Courier New";color:black">;
</span><span style="font-size:12.0pt;font-family:"Courier New";color:forestgreen">% test statistic that will be evaluated under the permutation distribution.
</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:12.0pt;font-family:"Courier New";color:black">cfg.minnbchan = 1;
</span><span style="font-size:12.0pt;font-family:"Courier New";color:forestgreen">% minimum number of neighborhood channels that is required for a selected
</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:12.0pt;font-family:"Courier New";color:black"> </span><span style="font-size:12.0pt;font-family:"Courier New";color:forestgreen">% sample to be included
in the clustering algorithm (default=0).</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:12.0pt;font-family:"Courier New";color:black">cfg.tail = 0;
</span><span style="font-size:12.0pt;font-family:"Courier New";color:forestgreen">% -1, 1 or 0 (default = 0); one-sided or two-sided test</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:12.0pt;font-family:"Courier New";color:black">cfg.clustertail = 0;</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:12.0pt;font-family:"Courier New";color:black">cfg.alpha = 0.05;
</span><span style="font-size:12.0pt;font-family:"Courier New";color:forestgreen">% alpha level of the permutation test</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:12.0pt;font-family:"Courier New";color:black">cfg.numrandomization = 1000;
</span><span style="font-size:12.0pt;font-family:"Courier New";color:forestgreen">% number of draws from the permutation distribution</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:12.0pt;font-family:"Courier New";color:black">cfg.neighbourdist = 0.2;</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:12.0pt;font-family:"Courier New";color:forestgreen">%cfg.neighbours = cfg_n;</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:12.0pt;font-family:"Courier New";color:black">cfg.channel = {</span><span style="font-size:12.0pt;font-family:"Courier New";color:#A020F0">'all'</span><span style="font-size:12.0pt;font-family:"Courier New";color:black">,
</span><span style="font-size:12.0pt;font-family:"Courier New";color:#A020F0">'-HEOG'</span><span style="font-size:12.0pt;font-family:"Courier New";color:black">,
</span><span style="font-size:12.0pt;font-family:"Courier New";color:#A020F0">'-VEOG'</span><span style="font-size:12.0pt;font-family:"Courier New";color:black">,
</span><span style="font-size:12.0pt;font-family:"Courier New";color:#A020F0">'-EKG'</span><span style="font-size:12.0pt;font-family:"Courier New";color:black">};</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:12.0pt;font-family:"Courier New";color:black">cfg.latency = [0. 0.5];</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:12.0pt;font-family:"Courier New";color:black">cfg.layout =
</span><span style="font-size:12.0pt;font-family:"Courier New";color:#A020F0">'C:\Matlab_programs\Fieldtrip\My_Fieldtrip\EEG1010_modified32.lay'</span><span style="font-size:12.0pt;font-family:"Courier New";color:black">;</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:12.0pt;font-family:"Courier New";color:black"></span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:12.0pt;font-family:"Courier New";color:black"> </span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:12.0pt;font-family:"Courier New";color:black">subj1 = length(GROUP {nGroup1,1});</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:12.0pt;font-family:"Courier New";color:black">subj2 = length(GROUP {nGroup2,1});</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:12.0pt;font-family:"Courier New";color:black"></span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:12.0pt;font-family:"Courier New";color:black">design = zeros(1,subj1+subj2);</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:12.0pt;font-family:"Courier New";color:black">design(1,1:subj1) = 1;</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:12.0pt;font-family:"Courier New";color:black">design(1,subj1+1:subj1+subj2) = 2;</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:12.0pt;font-family:"Courier New";color:black"></span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:12.0pt;font-family:"Courier New";color:black">cfg.design = design;</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:12.0pt;font-family:"Courier New";color:black">cfg.ivar = 1;</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:12.0pt;font-family:"Courier New";color:black"></span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:12.0pt;font-family:"Courier New";color:black">[stat] = ft_timelockstatistics(cfg, peak1_gr1 , peak1_gr2 );</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">____________________________________________________________________________<o:p></o:p></p>
<p class="MsoNormal">Olga Sysoeva,<o:p></o:p></p>
<p class="MsoNormal">Research Associate, PhD<o:p></o:p></p>
<p class="MsoNormal">Psychiatry Department,<o:p></o:p></p>
<p class="MsoNormal">Washington University School of Medicine<o:p></o:p></p>
<p class="MsoNormal">Campus Box 8134<o:p></o:p></p>
<p class="MsoNormal">660 South Euclid Ave<o:p></o:p></p>
<p class="MsoNormal">Saint Louis, MO 63110-9909<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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