n-way anova produces the same p-value for all groups

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AbioEngineer
AbioEngineer 2021-6-30
回答： AbioEngineer 2022-6-5
I have 6 vectors of values. These are split into groups i and m. There are 3 i groups and 2 m groups, which yields a combination of 6 total groups. Supposedly, my data should indicate that the data I have are grouped better according to 'Hm' vs 'Rm' than 'Li' vs 'Ri' vs 'Hi'. When I run the ANOVA using anovan() I get the same P-value for the i grouping, the m grouping and i*m interaction. When I plot the distributions using a boxplot they are clearly more separable along the m dimension.
All necessary files are attached. I'm using R2021a
I am running:
mdacdlcdp=[cdlcdpLiRm;cdlcdpLiHm;cdlcdpRiRm;cdlcdpRiHm;cdlcdpHiRm;cdlcdpHiHm];
p=anovan(mdacdlcdp,{igroup,mgroup},'model','interaction','varnames',{'i','m'})
But the results shown below are not consistent with my expectations.
Source Sum Sq. d.f. Mean Sq. F Prob>F
-----------------------------------------------------------------
i 0.4867 2 0.24335 2.98 0.054
m 1.2762 1 1.27619 15.62 0.054
i*m 0.2255 2 0.11276 1.38 0.054
Error 11.7664 144 0.08171
Total 13.7548 149
  2 个评论
Megumi Fukuda
Megumi Fukuda 2021-7-1
I ran these codes with my computer (WIndows, MATLAB 2021a)
load('anovadata.mat')
load('igroup.mat')
load('mgroup.mat')
mdacdlcdp=[cdlcdpLiRm;cdlcdpLiHm;cdlcdpRiRm;cdlcdpRiHm;cdlcdpHiRm;cdlcdpHiHm];
p=anovan(mdacdlcdp,{igroup,mgroup},'model','interaction','varnames',{'i','m'})
and got these results. Could you confirm you run your code correctly?
Source Sum Sq. d.f. Mean Sq. F Prob>F
-----------------------------------------------------
i 0.4867 2 0.24335 2.98 0.054
m 1.2762 1 1.27619 15.62 0.0001
i*m 0.2255 2 0.11276 1.38 0.2549
Error 11.7664 144 0.08171
Total 13.7548 149
AbioEngineer
AbioEngineer 2021-7-1
Thank you for your reply. I ran the exact same code as you, copied and pasted from your response, but got the same results as before. Is there a low level problem with my computer? I also have 2020b installed, but it gives me the same results as 2021a. I have rebooted my PC too, but no luck.

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回答（1 个）

AbioEngineer
AbioEngineer 2022-6-5
One of the toolboxes I permanently added to my startup path was causing the problem. I muted all the starup addpaths and it worked like normal. Sorry for all the fuss

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