Re: [R] wilcox.test warnig message p-value where are the zeros in the data?

From: Peter Dalgaard <p.dalgaard_at_biostat.ku.dk>
Date: Fri 13 Jan 2006 - 02:28:17 EST

Knut Krueger <admin@biostatistic.de> writes:

> does anybody know why there are the two warnings in the example above?
>
> Regards Knut
>
> > day_4
> [1] 540 1 1 1 1 1 1 300 720 480
> > day_1
> [1] 438 343 1 475 1 562 500 435 1045 890
>
> > is.vector (day_1)
> [1] TRUE
> > is.vector (day_4)
>
> [1] TRUE
The paired Wilcoxon test depends on pairwise differences and as far as I can see you have two of those being zero, in cases 3 and 5.  

> > wilcox.test(day_4
> ,day_1,paired=TRUE,alternative="two.sided",exact=TRUE,conf.int=TRUE)
>
> Wilcoxon signed rank test with continuity correction
>
> data: day_4 and day_1
> V = 1, p-value = 0.02086
> alternative hypothesis: true mu is not equal to 0
> 95 percent confidence interval:
> -486.5 -120.0
> sample estimates:
> (pseudo)median
> -348
>
> Warning messages:
> 1: cannot compute exact p-value with zeroes in:
> wilcox.test.default(day_4, day_1, paired = TRUE, alternative =
> "two.sided",
> 2: cannot compute exact confidence interval with zeroes in:
> wilcox.test.default(day_4, day_1, paired = TRUE, alternative =
> "two.sided",
>
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-- 
   O__  ---- Peter Dalgaard             ุster Farimagsgade 5, Entr.B
  c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
 (*) \(*) -- University of Copenhagen   Denmark          Ph:  (+45) 35327918
~~~~~~~~~~ - (p.dalgaard@biostat.ku.dk)                  FAX: (+45) 35327907

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Received on Fri Jan 13 02:34:07 2006

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