[R-sig-eco] post hoc in Kruskal Wallis

[Dave Roberts]

If the design is balanced this function will work

npcompare <- function (var,class)
{
     k <- length(table(class))
     n <- length(var)/k

     se <- sqrt((n*(n*k)*(n*k+1))/12)
     rvar <- rank(var)

     for (i in 1:(k-1)) {
         left <- sum(rvar[as.numeric(class)==i])
         for (j in (i+1):k) {
             right <- sum(rvar[as.numeric(class)==j])
             diff = abs(left-right)
             cat(paste(i,j,left,right,diff,round(1-pt(diff/se,k),4),'\n'))
         }
     }
     cat('\n')
}

It's not formatted very elegantly, but it works.

Dave R.

On 11/24/2011 08:01 AM, Richard L. Boyce wrote:
> Zar, in Biostatistical Analysis, has a Tukey-like test that is highly
> recommended. You may need to do it by hand, but it is quite easy.
>
>> Message: 5
>> Date: Wed, 23 Nov 2011 18:21:54 +0100
>> From: "Jakub Szymkowiak"<qbaszym at tlen.pl>
>> To:<r-sig-ecology at r-project.org>
>> Subject: [R-sig-eco]  post hoc in Kruskal Wallis
>> Message-ID:<C8041F4B78EB487C8707E72114C3F4CF at komp>
>> Content-Type: text/plain; format=flowed; charset="iso-8859-1";
>> 	reply-type=original
>>
>> Hi,
>> does anyone know, how can I perform post-hoc tests (especially Least
>> Significant Difference and Sheffe Test) for results from Kruskal-Wallis
>> test? In KruskaI-Wallis test I found some significant differences between
>> tested groups, but I want to know between which groups this difference is
>> really signifficant.
>>
>> Cheers,
>> Jakub
>

-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
David W. Roberts                                     office 406-994-4548
Professor and Head                                      FAX 406-994-3190
Department of Ecology                         email droberts at montana.edu
Montana State University
Bozeman, MT 59717-3460