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


From   David Greenberg <dg4@nyu.edu>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: RE: When is the t-test appropriate?
Date   Thu, 29 Aug 2002 15:00:49 -0400

The t-test can be used with small samples, but then the underlying population must be normal. An issue not raised in other postings in response to this inquiry is that with such small samples, any test will have very low statistical power. The chances of failing to reject the null hypothesis when it is false will be high. David Greenberg, Sociology Department, New York University. 

----- Original Message -----
From: Lee Sieswerda <Lee.Sieswerda@tbdhu.com>
Date: Thursday, August 29, 2002 2:48 pm
Subject: st: RE: When is the t-test appropriate?

> 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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