bugPSPP - Bugs: bug #47041, Mann Whitney U test results are...

 
 

bug #47041: Mann Whitney U test results are not correct

Submitted by:  None
Submitted on:  Mon 01 Feb 2016 03:02:06 PM UTC  
 
Category: Numerical ErrorsSeverity: 5 - Average
Status: FixedAssigned to: None
Open/Closed: ClosedRelease: None
Effort: 0.00

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Fri 05 Feb 2016 03:08:05 PM UTC, comment #6:

I pushed a fix for this.

Thank you for reporting the problem.

John Darrington <jmd>
Project Administrator
Wed 03 Feb 2016 06:53:53 PM UTC, comment #5:

Confirmed.

It seems that pspp is not ignoring the cases which do not belong to either group.

We will fix this soon.

In the meantime, you can work around this problem by adding a line like:

SELECT IF (bolum = 1) OR (bolum = 2).

before you call NPAR TESTS.

John Darrington <jmd>
Project Administrator
Wed 03 Feb 2016 06:35:36 PM UTC, comment #4:

Thank you for your interest, here is the output:

Mann-Whitney Test
Ranks
|-----|----------------|--|---------|------------|
| |bolum |N |Mean Rank|Sum of Ranks|
|-----|----------------|--|---------|------------|
|tutum|Fen ve Tekn.Öğrt|33|35,00 |1155,00 |
| |----------------|--|---------|------------|
| |İngilizce Öğrt. |39|37,77 |1473,00 |
| |----------------|--|---------|------------|
| |Total |72| | |
|------------------------------------------------|

Test Statisticsa
|----------------------|--------|
| |tutum |
|----------------------|--------|
|Mann-Whitney U |594,000 |
|----------------------|--------|
|Wilcoxon W |1155,000|
|----------------------|--------|
|Z |-,560 |
|----------------------|--------|
|Asymp. Sig. (2-tailed)|,576 |
|-------------------------------|
a Grouping Variable: bolum

Eren Can Aybek <aybek>
Wed 03 Feb 2016 06:17:45 PM UTC, comment #3:

Thanks for the bug report.

Can you send the output from the other software for this dataset, so that we can compare them and work out what is happening.

John Darrington <jmd>
Project Administrator
Wed 03 Feb 2016 05:27:16 PM UTC, comment #2:

It seems that when I have only two groups to compare (e.g. male, female) there is no problem.

But when I have 2+ groups to compare (e.g. elementary, high school and university) and I only want to compare two groups, mean rank and sum of ranks are different as well as U, W and p values.

Since Kruskal-Wallis H test doesn't have post-hoc tests, I need to compare each group via Mann-Whitney U.

You can download the sample data from http://ab.olcme.net/pspp/02%20-%20Veriler/04%20-%20ANOVA.sav

I run:

NPAR TESTS
/M-W tutum by bolum(1,2)

And results are different with the results of other softwares.

Thank you.

Eren Can Aybek <aybek>
Mon 01 Feb 2016 06:26:02 PM UTC, comment #1:

Which values appear different?

Can you post some examples?

John Darrington <jmd>
Project Administrator
Mon 01 Feb 2016 03:02:06 PM UTC, original submission:

Hi,

When I run Mann Whitney U test, results are not matched with the results from other statistical softwares. Besides, I tried to use Kruskal-Wallis test for 2 group, and Kruskal-Wallis results are matched with the results of other statistical softwares.

I realized that this error occurs with stable versions and nightly builds.

I use Kruskal-Wallis for two groups instead of Mann Whitney U test for now. But it comes with practical issues (e.g. when I try to compare group 1 and group 3, I have to recode groups to different variable, because K-W includes group 2 too.)

Anonymous

 

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Attach File(s):
   
   
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Attached Files
file #36242:  Mann Whitney U.txt added by aybek (6KiB - text/plain - Output from another software.)

 

Depends on the following items: None found

Items that depend on this one: None found

 

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  • -unavailable- added by aybek (Posted a comment)
  • -unavailable- added by jmd (Posted a comment)
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    Follow 4 latest changes.

    Date Changed By Updated Field Previous Value => Replaced By
    Fri 05 Feb 2016 03:08:05 PM UTCjmdStatusConfirmed=>Fixed
      Open/ClosedOpen=>Closed
    Wed 03 Feb 2016 06:53:53 PM UTCjmdStatusNone=>Confirmed
    Wed 03 Feb 2016 06:37:00 PM UTCaybekAttached File-=>Added Mann Whitney U.txt, #36242

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