Dear all,

 

Great! Thanks for your fast response. You are right. The missing-analysis in
SPSS made the difference and was included as standard.

 

In future I will do missing-analysis in PSPP separately, thanks a lot.

 

Have a nice week.

 

Kind regards,

Mandy Nuszbaum

 

Von: Dr. Oliver Walter [mailto:o.wal...@psychometrie-online.de] 
Gesendet: Montag, 6. März 2017 14:38
An: pspp-users@gnu.org; wahrnehmung.experim...@gmx.de;
j...@darrington.wattle.id.au
Betreff: Error in computation of Mann-Whitney-U Test seems to be identified

 

Dear Prof. Nuszbaum,

you were right: There seems to be a problem and I think that I found it. The
missing data subcommand /MISSING=ANALYSIS does not seem to be working
properly. Although it should exclude cases with missing data for each
analysis (hence, it is called ANALYSIS) it does not do it. It seems to
include these cases in the U test analyses instead of excluding them. When I
assigned ranks to cases using the RANK VARIABLES command the ranks PSPP
built were the same as in SPSS. But in the U test analyses the ranks differ.


You may ask why this subcommand is important here, because you did not use
it in your syntax. I think it is the default setting and has not to be
written explicitely. Hence, PSPP uses it automatically.

When I excluded cases with missing data manually (I deleted them) and later
by the subcommand /MISSING = LISTWISE the results of PSPP were the same as
in SPSS and R (I checked R's results for variable I002_01 only).

Hence, PSPP developers should check the missing data subcommand
/MISSING=ANALYSIS in the NPAR command and correct it.

In the meantime we - you, your students and others - can run U test analyses
*** for each variable separately *** and use the subcommand
/MISSING=LISTWISE. Then the results should be the same as in SPSS. I checked
it using your data set and they were the same. The commands are

NPAR TESTS
/STATISTICS=DESCRIPTIVES
/MISSING=LISTWISE
/MANN-WHITNEY = I002_01  BY sum_HL (0 1) .

NPAR TESTS
/STATISTICS=DESCRIPTIVES
/MISSING=LISTWISE
/MANN-WHITNEY = I002_02  BY sum_HL (0 1) .

NPAR TESTS
/STATISTICS=DESCRIPTIVES
/MISSING=LISTWISE
/MANN-WHITNEY = I002_03  BY sum_HL (0 1) .

NPAR TESTS
/STATISTICS=DESCRIPTIVES
/MISSING=LISTWISE
/MANN-WHITNEY = I002_04  BY sum_HL (0 1) .

for your data set and analyses.

I attached the results in a pdf file (html output was strangely not working
for this output) and you could compare them to your results of SPSS.

Kind regards,

Oliver Walter

 

 

 

Am 06.03.2017 um 13:10 schrieb Mandy Nuszbaum:

Dear Oliver Walter,

 

I attached a shortened data file and Output (Copy in Excel including
syntax). The data base is not very large but results should be the same, or?
Maybe it’s my fault by doing the analysis.

 

The independent Variables are I002_01 to I002_04. The group variable is
sum_HL with groups 0 and 1. 

 

John Darrington mentioned, that there was an error, which was fixed (“I
suspect this is bug 47041 which has been fixed about a year ago”). So, I
installed PSPP new and did the analysis again (see Excel file).

 

I have installed the version: pspp-20160927-daily-32bits-setup.exe

 

Hope you can help, because my students use pspp and I like to be sure that
they get correct data output. The attached data is from such a student
project.

 

Thanks for your fast response.

 

Kind regards,

Mandy Nuszbaum

 

 

Von: Dr. Walter Statistics [mailto:i...@walter-statistics.com] 
Gesendet: Samstag, 4. März 2017 19:51
An: pspp-users@gnu.org <mailto:pspp-users@gnu.org> ;
wahrnehmung.experim...@gmx.de <mailto:wahrnehmung.experim...@gmx.de> 
Betreff: Re: Error in computation of Mann-Whitney-U Test

 

Dear Prof. Nuszbaum,

your question would be easier to answer if you described it in more detail,
e.g. by posting your outputs and / or your data sets (if the sample sizes
are small, we could compare the results).

Kind regards

Oliver Walter

---
Dr. Walter Statistics
Gabelsberger Straße 27
24148 Kiel

Am 04.03.2017 um 19:20 schrieb Mandy Nuszbaum:

Dear all,

 

I computed Mann-Whitney-U using PSPP and SPSS and compared the results using
different data sets. Results are completely different and led to wrong
conclusions. 

 

Can anyone fix the problem?

 

Kind regards,

mn







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