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st: RE: mann-whitney test


From   "Feiveson, Alan H. (JSC-SK311)" <alan.h.feiveson@nasa.gov>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: mann-whitney test
Date   Fri, 5 May 2006 08:18:31 -0500

Stefania 

I think what you need is the _collapse_ command to produce the group
averages. Then you could run the Mann Whitney on those. However if it is
the same group for two different periods, you need a paired comaprison
such as the signed rank test. Actually, since your basic variable is a
group mean, a normal assumption may be OK even if the original data is
non-normal, and you could use the more powerful paired t-test. 

A Feiveson

-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of
ottone@unipmn.it
Sent: Thursday, May 04, 2006 10:05 AM
To: statalist@hsphsun2.harvard.edu
Subject: st: mann-whitney test

Sorry, but I'm confused! I ran two treatments and  32 subjects
(organised in group of 4) participated to each treatment (10 periods).
This means that I have only 8 independent observations in each period
for each treatment. How should be my dataset to run the mann-whitney
test? If I consider 320 observations in each treatment, I cannot say
that they are independent. How should I perform the test in this case?

stefania ottone



> There is some misunderstanding here, I guess.
>
> Mann-Whitney requires at a minimum all the individual ranks. It can't 
> work on just input of averages, or even medians.
>
> Nick
> n.j.cox@durham.ac.uk
>
> ottone@unipmn.it
>
>> I have to run the mann-whitney test to check the difference in the 
>> trend between two treatments in a public good game experiment.
>> This test has to be run on average contributions of groups.
>> Does it mean
>> that I should have in my dataset a single observation for each group 
>> that represents the average contribution of the group over all the 
>> periods?
>
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