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st: -nlogit- question


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: -nlogit- question
Date   Fri, 29 Feb 2008 14:18:54 -0000

This is forwarded on behalf of Jared Gross. 

----------------------------------------------------

Please forgive my basic question; relative to most users on this list,
I'm
not very familiar with Stata.

I'm trying to use the nlogit command in Stata 10 to estimate a
degenerate
model of mergers and acquisitions.  Unfortunately, I keep getting the
error
"no cases remain after removing invalid observations."  Because I'm
pretty
sure I'm mis-specifying my model, and possibly don't have the cases
right,
I'm hoping someone here can help.

My data looks like the following:

Ticker	Year 	Covariates 	GoesPrivate 	PublicTakeover 	Event
ContinuesIndep

A		1999	x		0			0
0		1	
A		2000	x		0			1
1		0		
B		1998	y		0			0
0		1		
B		1999	z		0			0
0		1
B		2000	z		1			0
2		0


And the model I want to estimate is:

Company either (1) has  ContinuesIndependently == 1 OR (2) is subject to
Event == 1 | Event == 2

If Event == 1 | Event == 2, then either (A) GoesPrivate == 1 OR (B)
PublicTakeover == 1,

so that I have a nested model in which the first logit determines
whether a
company continues in my data to the next year or exits through
"Takeover"
(i.e. Event == 1 | Event == 2); and then a second, degenerate stage in
which
the company, if Takeover == 1, either GoesPrivate == 1 or PublicTakeover
==
1.

How do I estimate this?  I tried to use the following commands:


egen id = group(ticker)
nloitgen takeoverType = Event(Cont: 0, takeover: 1|2)
nlogit GoesPrivate covariates || takeoverType: other_covariates,
base(cont)
||, case(id)

I think my problem may be coming stemming from my use of ticker as the
case(id).


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