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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