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Re: st: Fisher's exact test


From   Ronan Conroy <rconroy@rcsi.ie>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   Re: st: Fisher's exact test
Date   Tue, 13 Sep 2011 11:32:59 +0100

On 2011 MFómh 12, at 17:52, Beatrice Crozza wrote:

> I would like to compute the ratio between the mean trading volume
> around announcements and the mean trading volume at the same time of
> the day on non-announcement days.
> I want than to test if these two means are significantly different at 5% level.
> 
> I read this post:
> http://www.ats.ucla.edu/stat/stata/whatstat/whatstat.htm
> Since when there is the news I have only 5 obs, I want to use the
> Fisher’s exact test.

If you only have five observations there is a very good chance that an effect size that would be considered of real life importance would go undetected in your data. With five observations, you probably have a case series rather than a statistical sample. 

Ronán Conroy
rconroy@rcsi.ie
Associate Professor
Division of Population Health Sciences
Royal College of Surgeons in Ireland
Beaux Lane House
Dublin 2


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