[R] Letter-based representation of pairwise comparisons

[David Winsemius]

On Oct 6, 2009, at 8:41 AM, goz wrote:

>
> hello,
>
> i try to use the multcomp letters, but i have problems with my  
> results :
>
> here is my pvalue matrix (from a pairwise.t.test) :
>
> pair=pairwise.t.test(...)
> pair$p.value
>
>        0           B            BxS
> B    0.01727    -             -
> BxS 0.00013    0.00226   -
> S    0.87555    0.02610   0.00027
>
>
> i was thiking to have something like that :
> 0  B  S  BxS
> a  b  a  c
>
> but function return :
>
>> multcompLetters(pair$p.value)
>  B   BxS   S
> "a"  "b"   "a"
>
>
> first question : why the 0 traitement doesn't appears in result ?

But there is a "0" column. <???>

> second  : why the results differs than what i expected ?

Because your understanding of what it means to have "pairwise"  
comparisons differs from that of the author's.


>
> many thanks.
>
> -- 
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David Winsemius, MD
Heritage Laboratories
West Hartford, CT