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Re: st: Numerous t-tests
At 16:51 26/10/2005, Michael wrote:
-regress- has a -robust- option to handle unequal variances. However, it is
a valid point that (unlike -ttest-) -regress- does not use a
Sattertwhaite-corrected degrees of freedom formula, so there is the danger
that confidence intervals will be over-conservative at small sample sizes.
"Ronán Conroy" <firstname.lastname@example.org> wrote:
-regress- is a lot faster than t-test, and the output is easier to read,
IMO. The coefficient and its confidence interval represent
the difference in means and its CI.
While I agree that regress is faster and often preferred to t-tests, one
should be aware that regress will assume equal variances for the two
groups identified by the dummy variable. That assumption may or may not
be what you want.
For what it's worth, my own -metaparm- package (downloadable from SSC) can
be used with -regress- and -parmest- to produce Satterthwaite confidence
intervals for differences between means. I sometimes use it for calculating
confidence intervals for a ratio of geometric means, allowing for unequal
coefficients of variation.
I hope this helps.
Lecturer in Medical Statistics
Department of Public Health Sciences
Division of Asthma, Allergy and Lung Biology
King's College London
5th Floor, Capital House
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Opinions expressed are those of the author, not the institution.
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