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Re: st: Parameters returned by -lincom- after -logistic-


From   Roger Newson <roger.newson@kcl.ac.uk>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Parameters returned by -lincom- after -logistic-
Date   Sun, 08 May 2005 18:48:25 +0100

Thanks to Richard for warning us about this little quirk re -lincom- after -svy- commands in Stata 8. This is controlled by the undocumented Stata 8 command -is_svy-, which you can find out about by typing

whelp is_svy

I think I will do something about the -svy- feature in the coming Stata 8 version of -lincomest-, which I will write after fixing the feature re -logistic- in the final Stata 7 version of -lincomest-. In the meantime, I am scanning through the Stata 8 -lincom- and seeing if I can find any more hazardous features like these.

Roger


At 20:36 06/05/2005, Richard Williams wrote:

At 08:20 PM 5/6/2005 +0100, Roger Newson wrote:
Hello All (especially StataCorp)

I am still using Stata 8.2 under Windows 2000, and have just found out about the behaviour of -lincom- if invoked after -logistic-, whereby it returns in -r()- an exponentiated estimate and its asymptotic standard error, even if the user has not specified any of the options -eform-, -or-, -hr-, -irr- or -rrr-. (See -[R] lincom- in the Stata 8 manuals.) This is a problem, because my own -lincomest- package (downloadable from SSC) invokes -lincom- without any estimation options, and attempts to use the estimate -r(estimate)- and its standard error -r(stderr)- to calculate a 1x1 matrix of estimates and a 1x1 variance matrix to be stored in the estimation results, and then lists the estimation results, using -eform()- only if specified by the user. (See Newson (2003) for more about -lincomest-.)
Further, perhaps I am missing it, but I don't see anything like an xb option that could force the behavior you want. I suppose you would have to add lines to your program to make sure it was doing what you wanted.

Another little quirk I discovered in Stata 8: After most commands, lincom returns its result in r(estimate). But, after svy commands, it returns its result in r(est). This was screwing up one of my programs until I figured out what was going on. I asked tech support if there was any particular reason for this and they said no, but they added that this would not be an issue in Stata 9.

I think with returns, consistency is very important. With regular commands, you can often support both old and new syntax; but if you change the behavior/names of returns or do things inconsistently across programs it can create problems.


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Richard Williams, Notre Dame Dept of Sociology
OFFICE: (574)631-6668, (574)631-6463
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--
Roger Newson
Lecturer in Medical Statistics
Department of Public Health Sciences
Division of Asthma, Allergy and Lung Biology
King's College London

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Opinions expressed are those of the author, not the institution.

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