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From |
"Martin Weiss" <martin.weiss1@gmx.de> |

To |
<statalist@hsphsun2.harvard.edu> |

Subject |
st: RE: the sign of z statatistic after -ranksum-? |

Date |
Sun, 25 Oct 2009 10:22:36 +0100 |

<> Have you had a look at "Methods and formulas" for -ranksum-, which is quite comprehensive? See [R], p. 1477. In any case, the test is against a two-sided alternative, so the sign hardly matters... HTH Martin -----Original Message----- From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of gjhxmu@sina.com Sent: Sonntag, 25. Oktober 2009 04:29 To: statalist Subject: st: the sign of z statatistic after -ranksum-? Dear statalists, I use -ranksum- in the stata to do the Wilcoxon rank-sum test, which is also known as the Mann-Whitney two-sample statistic. My typing is as followings, webuse fuel2,clear ranksum mpg, by(treat) // the z statistic equals -1.279 replace treat=treat==0 ranksum mpg, by(treat) // the z statistic equals 1.279 My doubt is why the sign of z statistic is opposite. As far as I know, in the computation of z statistic the result should be the same no matter which group is compared with which group. Any help will be appreciated! Best regards, Rose. * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/ * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**References**:**st: the sign of z statatistic after -ranksum-?***From:*gjhxmu@sina.com

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