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


From   Michael Alexander <Michael.Alexander@aifs.gov.au>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: RE: RE: outreg/estimates type commands for ttest
Date   Fri, 25 Aug 2006 09:48:04 +1000

Roger

Thanks for the suggestions re downloading stuff from your website. I actually tried to access using the -net- command in stata and came across a small glitch in the links. After the command -net from http://www.imperial.ac.uk/nhli/r.newson/- the user is presented with seven highlighted web links (stata5-stata9 papers usergp) and clicking on anyone of them takes you to the appropriate place to download the files. However, if you try and then go to any of the other links, stata seems to remember the previous file path and just adds the new final destination folder to end. For example, if I go to the papers link first (no problems) followed by the usergp link, you get the following error:

file http://www.imperial.ac.uk/nhli/r.newson/papers/usergp/stata.toc not found
http://www.imperial.ac.uk/nhli/r.newson/papers/usergp/ either
1) is not a valid URL, or
2) could not be contacted, or
3) is not a Stata download site (has no stata.toc file).

I tested it for a few different combinations (stata9 then papers, papers then stata9, usergp then stata9) after restarting Stata and each time it would allow me to go to the first link but then error on second, and the error message would be similar to the above with the first link folder somehow embedded in the filepath.

I have now resorted to accessing the files directly with my browser but thought you would want to know about the glitch.

Michael

Newson, Roger B 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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--
Michael Alexander
Principal Research Fellow
Australian Institute of Family Studies

300 Queen Street Melbourne VIC 3000

Tel: 03 9214 7841
Fax: 03 9214 7839
Mob: 0419 406 078
Email: Michael.Alexander@aifs.gov.au
Web-site: www.aifs.gov.au

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