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st: RE: When is the t-test appropriate?


From   Lee Sieswerda <Lee.Sieswerda@tbdhu.com>
To   "'statalist@hsphsun2.harvard.edu'" <statalist@hsphsun2.harvard.edu>
Subject   st: RE: When is the t-test appropriate?
Date   Thu, 29 Aug 2002 14:48:06 -0400

The t-test doesn't require the underlying population to be normal, but it
does require that you have a good sized sample. I assume that, since you
wanted to do a t-test, your data are continuous. For that, you want the
Wilcoxon/Mann-Whitney rank-sum test (help ranksum).
If you don't like that, apparently StatXact has about a million small-sample
exact tests. That way you can really shop around until you find a
statistically significant result :)
Best,
Lee

Lee Sieswerda, Epidemiologist
Thunder Bay District Health Unit
999 Balmoral Street
Thunder Bay, Ontario
Canada  P7B 6E7
Tel: +1 (807) 625-5957
Fax: +1 (807) 623-2369
Lee.Sieswerda@tbdhu.com
www.tbdhu.com



> -----Original Message-----
> From:	Jon Wainwright [SMTP:jwainwright@austin.rr.com]
> Sent:	Thursday, August 29, 2002 12:20 PM
> To:	statalist@hsphsun2.harvard.edu
> Subject:	st: When is the t-test appropriate?
> 
> Dear Statalist,
> 
> I would like to compare the means of two very small random samples (n1=3,
> n2=7). Both samples were drawn from populations of unknown distribution.
> Is
> Stata's ttest appropriate in such a situation, or does it require the
> underlying populations to be normally distributed?  If ttest is not
> appropriate, can anyone suggest are more appropriate method for testing
> the
> difference of the means?
> 
> Thanks for your help.
> 
> Jon Wainwright
> Austin, Texas
> 
> -- 
> 
> 
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