[R] Post-Hoc tests for Friedman Test?

[David Winsemius]

On Sep 20, 2009, at 9:35 PM, David Winsemius wrote:

>
> On Sep 20, 2009, at 9:05 PM, jon at terraspark.com wrote:
>
>> Hi there all,
>>
>> This is my first post to the list and I'll first say a few things:
>> - R is great!
>> - The archives of this list have helped me solve all of my problems/ 
>> questions so far
>> - I only know enough statistics "to be dangerous"
>>
>> I'm looking for a way to do post-hoc tests for the Friedman test. I  
>> have a dataset from a within-subjects design with 5 conditions  
>> where some of the dependent variables are ordinal, resulting from  
>> (summed) likert-scaled questionnaire data.
>>
>> From what I've read, I could use a wilcox.test on pairs of  
>> conditions and adjust the p level, but is there something in R that  
>> does a better job/automates this.
>>
>> I've seen references to the npmc package but that doesn't seem to  
>> do what I'm looking for, because it only accepts a data frame with  
>> two columns - i.e. there's no way to specify grouping/subject  
>> identifiers.
>>
>> Thanks,
>
> There is a worked example in the coin package for using a  
> permutation test to examine differences after a Friedman test. The  
> authors, Hothorn , Hornik , van de Wiel, and Zeileis, call this  
> method the Wilcoxon-Nemenyi-McDonald-Thompson test and cite:  
> Hollander & Wolfe (1999), page 295
>
> http://finzi.psych.upenn.edu/R/library/coin/html/SymmetryTests.html


A further option just presented itself during a search for an  
unrelated question:

The MTP function in the multtest package has a robust=TRUE set of  
methods with these equivalencies offered:

t.onesamp or t.pair:
	Wilcoxon signed rank, wilcox.test with y=NULL or paired=TRUE,
t.twosamp.equalvar:
	Wilcoxon rank sum or Mann-Whitney, wilcox.test,
f: 		Kruskal-Wallis rank sum, kruskal.test,
f.block:	Friedman rank sum, friedman.test,
f.twoway:	Friedman rank sum, friedman.test,

http://finzi.psych.upenn.edu/R/library/multtest/html/MTP.html

-- 

David Winsemius, MD
Heritage Laboratories
West Hartford, CT