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Re: st: RE: RE: outreg/estimates type commands for ttest


From   Nishant Dass <nishant_dass@yahoo.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: RE: RE: outreg/estimates type commands for ttest
Date   Thu, 24 Aug 2006 08:12:02 -0700 (PDT)

Hello Roger,

Although I was not using the regression as was described by
Nick in his reply, it's good to know the precise difference
between the two options of -ttest-.  Thanks a lot for the
clarification.  

Regards,

Nishant



--- "Newson, Roger B" <r.newson@imperial.ac.uk> wrote:

> Nick Cox wrote:
> **** Beginning of quote
> In the case of t tests, a work-around is obtained
> by noting that the results of 
> 
> regress <response> <binary variable>
> 
> are equivalent to 
> 
> ttest <response>, by(<binary variable>) 
> 
> so that -outreg- or -estout- (which I think 
> you mean here rather than -estimates-) can then be 
> used. 
> *** End of quote
> 
> This is the case if the user wanted an equal-variance
> t-test. However,
> if the user wanted an unequal-variance t-test (complete
> with
> Satterthwaite corrected degrees of freedom), then the
> results are not
> quite equivalent.
> 
> It is possible to do unequal-variance t-tests with
> Satterthwaite degrees
> of freedom, saving the results, using -regress-, -parmby-
> and
> -metaparm-. For instance, in the -auto- data, the user
> can type
> 
> . sysuse auto, clear
> . parmby "regress weight", by(foreign) norestore
> . gene byte iwt=!foreign-foreign
> . tempfile tf1
> . metaparm [iwei=iwt] , saving(`tf1', replace)
> . append using `tf1'
> . list
> 
> This replaces the -auto- data in memory with a new
> dataset (or
> resultsset), with 1 observation for each of 3 parameters
> (the mean
> weight for US cars, the mean weight for non-US cars, and
> the difference
> between those 2 means), and variables storing the
> estimates, degrees of
> freedom, confidence limits and P-values for these
> parameters. Such a
> dataset can then be processed further to produce an
> output table,
> possibly using the -listtex- package.
> 
> The packages -listtex-, -metaparm- and -parmest- (which
> includes
> -parmby-) are all downloadable from SSC. So are a lot of
> other packages
> which the user can use to generate plots and tables in
> Stata, using
> output datasets (or resultssets). More about how to use
> these packages
> can be found in Newson (2003) and in the Stata User
> Meeting
> presentations of Newson (2002), Newson (2004), Newson
> (2005) and Newson
> (2006), all of which can be downloaded from ny website at
> 
> http://www.imperial.ac.uk/nhli/r.newson/
> 
> using either a browser or the -net- command in Stata.
> 
> I hope this helps.
> 
> Roger
> 
> 
> References
> 
> Creating plots and tables of estimation results using
> parmest and
> friends. Presented at the 8th UK Stata User Meeting,
> 20-21 May, 2002.
> 
> Newson R. Confidence intervals and p-values for delivery
> to the end
> user. The Stata Journal 2003; 3(3): 245-269.
> 
> Newson R. From datasets to resultssets in Stata.
> Presented at the 10th
> UK Stata User Meeting, 28-29 June, 2004.
> 
> Newson R. Generalized confidence interval plots using
> commands or
> dialogs. Presented at the 11th UK Stata User Meeting,
> 17-18 May, 2005.
> 
> Newson R. Resultssets, resultsspreadsheets and
> resultsplots in Stata.
> Presented at the 4th German Stata User Meeting, 31 March,
> 2006.
> 
> *
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