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Topic: How to get p-values from multcompare?
Replies: 5   Last Post: Jun 18, 2015 6:37 AM

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Markus Due Jakobsen

Posts: 43
Registered: 4/29/08
How to get p-values from multcompare?
Posted: Nov 10, 2008 4:55 AM
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When using Anova1 to test for differences between group, Anova 1 returns a p-value that shows whether there is a difference or not. To make a further pairwise comparison between groups you can use the multcompare-function. Is this some sort of post hoc test? It uses ‘tukey-kramer’ as default ..
How is it possible to get the p-values of each pairwise comparison?
A multcompare example:
strength = [82 86 79 83 84 85 86 87 74 82 78 75 76 77 79 79 77... 78 82 79];
alloy = {'st','st','st','st','st','st','st','st', ... 'al1','al1','al1','al1','al1','al1','al2','al2','al2','al2','al2','al2'};
[p,a,s] = anova1(strength,alloy);
[c,m,h,nms] = multcompare(s);
Holm.m from file exchange uses Holm-Sidak procedure for multiple Student's t tests to compare differences between groups. This m-file show all comparisons with p-values:

% Test p-value alpha Comment
% 1-4 0.0013 0.0085 Reject Ho
% 1-3 0.0078 0.0102 Reject Ho
% 1-2 0.0553 0.0127 Fail to reject Ho
% 2-4 0.1254 No comparison made Ho is accepted
% 2-3 0.3563 No comparison made Ho is accepted
% 3-4 0.5606 No comparison made Ho is accepted
Is it possible to do the same with multcompare? The information lies within the graph-output, however it is not included in the command-output.

Any suggestions

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