wilcox.test warnig message p-value where are the zeros in the data?

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wilcox.test warnig message p-value where are the zeros in the data?

Knut Krueger
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

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

Peter Dalgaard
Knut Krueger <[hidden email]> 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",
>
> ______________________________________________
> [hidden email] mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
>

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   O__  ---- Peter Dalgaard             Ă˜ster Farimagsgade 5, Entr.B
  c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
 (*) \(*) -- University of Copenhagen   Denmark          Ph:  (+45) 35327918
~~~~~~~~~~ - ([hidden email])                  FAX: (+45) 35327907

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