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RE: st: Post estimation power estimations.


From   Cameron McIntosh <cnm100@hotmail.com>
To   STATA LIST <statalist@hsphsun2.harvard.edu>
Subject   RE: st: Post estimation power estimations.
Date   Sat, 15 Oct 2011 12:37:21 -0400

What's the correlation between var1 and var2?

Cam
 


> From: lfolkestad@health.sdu.dk
> To: statalist@hsphsun2.harvard.edu
> Date: Sat, 15 Oct 2011 17:45:55 +0200
> Subject: st: Post estimation power estimations.
> 
> Evnin' list.
> 
> I have a question for you: when you do a ttest and you have no significant difference, you can estimate the group size needed for the between group differences to be significant, using SD and the differences in mean. I know this is a statistical no no - but lets save that discussion for another chain of emails.
> 
> My problem is that the between group difference is significant. When i correct for a variable, that shouldent interfere the between group difference dissaperes. 
> 
> What i've done:
> Xi: regress var1 var2 i.group
> _group_2 p=0.45
> Indicating that the Var2 adjusted var1 between group difference is no longer significant. I believe This is a power issue.
> 
> Can i aply the same logic as in ttest exemple, and if so - how to do that in Stata? 
> 
> Mvh
> Lars Folkestad
> 
> 
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