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Dunn's post hoc test

6 messages · Martin Henry H. Stevens, Iain Gallagher, Robert Baer +1 more

Original
Iain Gallagher
# 
Hi Everyone.

I am rather new to R and I've been trying to implement a function to 
carry out the above test. For a couple of days now I've been stuck on 
how to generate average rank differences.

Say I have a vector of average ranks:

averank<- c(2,5,9,12)

I would like to subtract averank[1] from averank[2], averank[1] and 
averank[2] from averank[3] and averank[1], averank[2] and averank[3] 
from averank[4] etc (I know the syntax is wrong here... it's just for 
illustration) but I can't work out how to do it.

Ideally I would like to generate an array showing the differences 
between the average ranks so I could tell at a glance which ones were 
greater than my critical value

I've been looking at loops etc but it's a little beyond me at the 
moment. Thanks for any suggestions.

Iain Gallagher
IIIR
Edinburgh University
Martin Henry H. Stevens
# 
I don't know Dunn's rank test, but the following substracts each of  
the sums of averanks from the next rank.

cumsum(averank)[-length(averank)] - averank[-1]

Hank
On Oct 17, 2005, at 4:30 AM, Iain Gallagher wrote:

            

      
      
      
    

        

      
      
    

        
Dr. Martin Henry H. Stevens, Assistant Professor
338 Pearson Hall
Botany Department
Miami University
Oxford, OH 45056

Office: (513) 529-4206
Lab: (513) 529-4262
FAX: (513) 529-4243
http://www.cas.muohio.edu/~stevenmh/
http://www.muohio.edu/ecology/
http://www.muohio.edu/botany/
"E Pluribus Unum"

  
  


  


      

    

    

      
      

        


  

        

      Iain Gallagher
    

    

      
      #
    

  


  

      
Thanks for your reply Hank. It's not really what I'm
after (though it's good to know).

For the test ( as described in Statistics for the
Biosciences by W. Gardiner. Prentice Hall, 1997) I
have to rank my groups, calculate the average rank,
then subtratc each average rank from every other. Any
value greater than the test statistic is significant.

eg average rank difference table:

   2     5     8    9
---|------------------  
2  -     3     6    7  
   |
5  -     -     3    4 
   |
8  -     -     -    1  
   |
9  -     -     -    -  
   |

I can't get my head around writing an algorithm for
this if I have a vector of average ranks eg averank<-
c(2,5,8,9).

I know I can address the vector by index and that this
is probably the correct route but I can't get the
indexing algorithm right! 

I'm sure someone will point out somethng simple and
I'll kick myself but the help would be appreciated. 

Thanks again.

Iain Gallagher

--- "Martin Henry H. Stevens" <HStevens at MUOhio.edu>
wrote:

            

      
      
      
    

        

      
      
    

        

      
      
    

  
  


  


      

    

    

      
      

        


  

        

      Robert Baer
    

    

      
      #
    

  


  

      
I think Martin told you the basic approach to the indexing:

averank<-sort(sample(1:100,25,replace=TRUE))
averank[-1] - averank[-length(averank)]
 [1]  1  1  6  3  4 14  1  1  8  1  2  6  5  4 10  0  3  2  1 11  1  1  2  0
averank
 [1]  4  5  6 12 15 19 33 34 35 43 44 46 52 57 61 71 71 74 76 77 88 89 90 92
92


----- Original Message ----- 
From: "IAIN GALLAGHER" <iaingallagher at btopenworld.com>
To: "Martin Henry H. Stevens" <HStevens at MUOhio.edu>
Cc: <r-help at stat.math.ethz.ch>
Sent: Monday, October 17, 2005 2:29 PM
Subject: Re: [R] Dunn's post hoc test

            

      
      
      
    

        

      
      
    

        

      
      
    

            

      
      
      
    

        

      
      
    

        
http://www.R-project.org/posting-guide.html

            

      
      
      
    

  
  


  


      

    

    

      
      

        


  

        

      Robert Baer
    

    

      
      #
    

  


  

      
I think I misunderstood your follow-up question.  Try this:

            

      
      
      
    

        
+ for (j in 1:length(averank)){
+ x[i,j] <- averank[i] - averank[j]
+ }}

            

      
      
      
    

        
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
 [1,]    0  -14  -15  -16  -16  -23  -37  -51  -67   -79
 [2,]   14    0   -1   -2   -2   -9  -23  -37  -53   -65
 [3,]   15    1    0   -1   -1   -8  -22  -36  -52   -64
 [4,]   16    2    1    0    0   -7  -21  -35  -51   -63
 [5,]   16    2    1    0    0   -7  -21  -35  -51   -63
 [6,]   23    9    8    7    7    0  -14  -28  -44   -56
 [7,]   37   23   22   21   21   14    0  -14  -30   -42
 [8,]   51   37   36   35   35   28   14    0  -16   -28
 [9,]   67   53   52   51   51   44   30   16    0   -12
[10,]   79   65   64   63   63   56   42   28   12     0

            

      
      
      
    

        
[1] 15 29 30 31 31 38 52 66 82 94



----- Original Message ----- 
From: "IAIN GALLAGHER" <iaingallagher at btopenworld.com>
To: "Martin Henry H. Stevens" <HStevens at MUOhio.edu>
Cc: <r-help at stat.math.ethz.ch>
Sent: Monday, October 17, 2005 2:29 PM
Subject: Re: [R] Dunn's post hoc test

            

      
      
      
    

        

      
      
    

        

      
      
    

            

      
      
      
    

        

      
      
    

        
http://www.R-project.org/posting-guide.html

            

      
      
      
    

  
  


  


      

    

    

      
      

        


  

        

      Hadley Wickham
    

    

      
      #
    

  


  

      
Or more simply:

averank<-sort(sample(1:100,10,replace=TRUE))
outer(averank, averank, "-")

Hadley

        
On 10/17/05, Robert Baer <rbaer at atsu.edu> wrote: