[R] [SPAM] Re: Different results on running Wilcoxon Rank Sum test in R and SPSS

[Michael Dewey]

See comments inline

On 19/01/2021 10:46, bharat rawlley wrote:
> Thank you for the reply and suggestion, Michael!
> 
> I used dput() and this is the output I can share with you. Simply 
> explained, I have 3 columns namely, drug_code, freq4w_n and PFD_n. Each 
> column has 132 values (including NA). The problem with the Wilcoxon Rank 
> Sum test has been described in my first email.
> 
> Please do let me know if you need any further clarification from my 
> side! Thanks a lot for your time!
> 
> structure(list(drug_code = c(0, 0, 1, 1, 1, 0, 0, 0, 1, 1, 0,
> 1, 0, 1, 0, 1, 1, 0, 0, 0, 1, 0, 1, 1, 0, 1, 0, 0, 0, 0, 0, 1,
> 0, 1, 0, 0, 1, 1, 0, 1, 1, 1, 1, 1, 0, 0, 1, 0, 1, 0, 0, 0, 1,
> 1, 0, 1, 1, 1, 0, 0, 0, 0, 1, 1, 1, 0, 0, 1, 1, 0, 0, 0, 0, 1,
> 0, 0, 1, 1, 1, 0, 1, 1, 0, 1, 1, 1, 0, 0, 1, 1, 1, 0, 0, 1, 0,
> 1, 1, 0, 1, 1, 0, 1, 0, 0, 1, 1, 1, 0, 0, 1, 0, 0, 1, 0, 0, 1,
> 1, 1, 1, 0, 0, 1, 0, 1, 0, 0, 1, 1, 1, 1, 0, 0), freq4w_n = c(1,
> NA, NA, 0, NA, 4, NA, 10, NA, 0, 6, NA, NA, NA, NA, NA, 10, NA,
> 0, NA, NA, NA, NA, 0, NA, 0, NA, NA, NA, 0, NA, 0, NA, NA, NA,
> NA, NA, NA, NA, NA, 0, 0, 12, 0, NA, 1, 2, 1, 2, 2, NA, 28, 0,
> NA, 4, NA, 1, NA, NA, NA, NA, NA, 0, 3, 1, NA, NA, NA, NA, 4,
> 28, NA, NA, 0, 2, 12, 0, NA, NA, NA, 0, NA, 0, NA, NA, NA, NA,
> NA, NA, NA, NA, NA, 3, NA, NA, NA, NA, NA, NA, 6, 1, NA, NA,
> NA, 0, NA, NA, NA, 0, 0, NA, 0, NA, 2, 8, 3, NA, NA, NA, 0, NA,
> NA, NA, 9, NA, NA, NA, NA, NA, NA, NA, NA), PFD_n = c(27, NA,
> NA, 28, NA, 26, NA, 20, NA, 30, 24, NA, NA, NA, NA, NA, 18, NA,
> 28, NA, NA, NA, NA, 28, NA, 28, NA, NA, NA, 28, NA, 28, NA, NA,
> NA, NA, NA, NA, NA, NA, 28, 28, 16, 28, NA, 27, 26, 27, 26, 26,
> NA, 0, 30, NA, 24, NA, 27, NA, NA, NA, NA, NA, 28, 25, 27, NA,
> NA, NA, NA, 26, 0, NA, NA, 28, 26, 16, 28, NA, NA, NA, 28, NA,
> 28, NA, NA, NA, NA, NA, NA, NA, NA, NA, 25, NA, NA, NA, NA, NA,
> NA, 22, 27, NA, NA, NA, 28, NA, NA, NA, 28, 28, NA, 28, NA, 26,
> 20, 25, NA, NA, NA, 30, NA, NA, NA, 19, NA, NA, NA, NA, NA, NA,
> NA, NA)), row.names = c(NA, -132L), class = c("tbl_df", "tbl",
> "data.frame"))
> 
> 
> Yours sincerely
> Bharat Rawlley
> On Tuesday, 19 January, 2021, 03:53:27 pm IST, Michael Dewey 
> <lists using dewey.myzen.co.uk> wrote:
> 
> 
> Unfortunately your data did not come through. Try using dput() and then
> pasting that into the body of your e-mail message.
> 
> On 18/01/2021 17:26, bharat rawlley via R-help wrote:
>  > Hello,
>  > On running the Wilcoxon Rank Sum test in R and SPSS, I am getting the 
> following discrepancies which I am unable to explain.
>  > Q1 In the attached data set, I was trying to compare freq4w_n in 
> those with drug_code 0 vs 1. SPSS gives a P value 0.031 vs R gives a P 
> value 0.001779.
>  > The code I used in R is as follows -
>  > wilcox.test(freq4w_n, drug_code, conf.int = T)

If I store your data in dat and then go

wilcox.test(freq4w_n ~ drug_code, dat)

I get a p-value of 0.031 agreeing with SPSS

The reason you are getting something different is that you are not 
specifying the first two parameters to wilcox.test() correctly.

>  >
>  >
>  > Q2 Similarly, in the same data set, when trying to compare PFD_n in 
> those with drug_code 0 vs 1, SPSS gives a P value 0.038 vs R gives a P 
> value < 2.2e-16.
>  > The code I used in R is as follows -
>  > wilcox.test(PFD_n, drug_code, mu = 0, alternative = "two.sided", 
> correct = TRUE, paired = FALSE, conf.int = TRUE)
>  >
>  >
>  > I have tried searching on Google and watching some Youtube tutorials, 
> I cannot find an answer, Any help will be really appreciated, Thank you!
> 
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> 
> -- 
> Michael
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Michael
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