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From: | Mandy Nuszbaum |
Subject: | AW: Error in computation of Mann-Whitney-U Test seems to be identified |
Date: | Tue, 7 Mar 2017 08:18:08 +0100 |
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:address@hidden 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 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:
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