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Re: st: Mean Test


From   Rijo John <rmjohn@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Mean Test
Date   Fri, 20 Jan 2006 23:59:01 +0530

I guess there is no concensus on using ttest with the welch's
correction when the variances are different. But I have been seeing
(at least so far) people using it like that. Now I dont know what to
do.  As I understand, when the variances are unequal one should do a
"Satterthwaite's Approximation F-test". The SAS's T-test procedure
reports both the equal variance and unequal variance cases in one
t-test command itself. But in stata (I guess) we need to explicitly
state the unequal option in the ttest. Which then essentially means
that we have to first test for the differences in variance and then
accordingly decide whether to put the unequal option or not. Then the
only difference that I see from my first post is using
"Satterthwaite's Approximation F-test" instead of welch's correction.

It would be nice if someone could kindly clarify this for me. If I am
right here can someone tell me how to recode my initial program so as
to incorporate three categories?

Thanks,
Rijo.


--
***************************************************
Rijo.M.John,Research Scholar
Indira Gandhi Institute of Development Research,
Film City Road, Goregaon East,
Mumbai, India-400065.
contact: (+91)9892412476
URL: http://rijojohn.bizhat.com

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