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Re: st: Help about Ranksum - porder option


From   Richard Goldstein <richgold@ix.netcom.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Help about Ranksum - porder option
Date   Mon, 31 Oct 2005 11:39:38 -0500

porder is taking all possible pairs (control=yes paired with each
control= no) and asking in what percent of those pairs is No larger than YES; this does not appear to be the question you are asking; if I correctly
understand your question, I think you want a parametric procedure rather than the rank-sum test

hope this helps
Rich

Óscar Becerra-CERAC wrote:


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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