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Re: st: linear probability model vs. probit/logit


From   Ronnie Babigumira <rb.glists@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: linear probability model vs. probit/logit
Date   Tue, 03 Oct 2006 22:58:32 +0200

Maarten, too late here as well to so Im gonna call it a day but before I do, I would like to ask you or anyone else a follow up question on this.

Does it make sense that Stata drops a variable that predicts perfectly and then goes ahead to drop the observations even when it does not use the problem variable in the regression? Any insights into what is going on.

This small example shows what I mean

------------ begin puzzle --------------
sysuse auto
gen bug = foreign
replace bug = 1 in 1/15
reg foreign price rep78 bug
logit foreign price rep78 bug
------------ end puzzle --------------

Ronnie

Maarten buis wrote:

At 03:04 PM 10/3/2006, Nishant Dass wrote:
> does perfect prediction result in exclusion of those observations?
--- Richard Williams <Richard.A.Williams.5@ND.edu> wrote:
Yes, but you should be getting a warning message about cases being dropped if that is what is happening.
I remembered that too, hence the link to the FAQ. But when I just now
repeated the example given in the FAQ, it did not drop any
observations. Anyhow, it is too late here in Europe to think clearly.
I'll think about it again in the morning.

Maarten

*----begin example----
sysuse auto, clear
drop if foreign==0 & gear_ratio>3.1
logit foreign mpg weight gear_ratio
*----end example----


-----------------------------------------
Maarten L. Buis
Department of Social Research Methodology
Vrije Universiteit Amsterdam
Boelelaan 1081
1081 HV Amsterdam
The Netherlands

visiting adress:
Buitenveldertselaan 3 (Metropolitan), room Z434

+31 20 5986715

http://home.fsw.vu.nl/m.buis/
-----------------------------------------





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