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st: Help about Ranksum - porder option


From   Óscar Becerra-CERAC <orbecerra@gmail.com>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: Help about Ranksum - porder option
Date   Mon, 31 Oct 2005 11:23:23 -0500

Hi all,

I am applying a Wilcoxon test for the equality of distributions, between two
control groups with the ranksum command. But I have a doubt about the
interpretation of the result of this test. The obtained result is:

ranksum series , by(control) porder

Two-sample Wilcoxon rank-sum (Mann-Whitney) test

  control    |      obs    rank sum    expected
-------------+---------------------------------
          NO |     2284     3280197     3338066
         YES |      638      990306      932437
-------------+---------------------------------
    combined |     2922     4270503     4270503

unadjusted variance   3.549e+08
adjustment for ties  -5118462.8
                     ----------
adjusted variance     3.498e+08

Ho: series(control==NO) = series(control==YES)
             z =  -3.094
    Prob > |z| =   0.0020

P{series(control==NO) > series(control==YES)} = 0.460


According with the p - value, I understand that the distribution between –
groups changes, but I can’t understand the result obtained by the p order
option. What I really want to know is if when my control measure is on it
has a positive impact in the behaviour of series. Can you help me with this?

Thanks,



Óscar Becerra
Researcher
 
Conflict Analysis Resource Center
Carrera 10 N° 65 - 35 Of. 603
Tels: +(571) 345 85 72/3
www.cerac.org.co


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