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Re: st: losing observations while correcting for selection bias using selmlog


From   "Joao Ricardo F. Lima" <jricardofl@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: losing observations while correcting for selection bias using selmlog
Date   Sat, 19 Apr 2008 12:11:33 -0300

Ramani,

please give us more information. How many observations do you have?
Are there missing values to the independent variables? Could you send

sum w3 $basefactors1 selmcat $selfactors

I used selmlog and with missing values, the program drop that observations.

Best,

Joao Lima

2008/4/19, Ramani Gunatilaka <ramani.gunatilaka@gmail.com>:
> Dear Statalist,
> I am using selmlog to estimate wage functions. The full sample is of
> labour market participants.
> For the multinomial logit part, I have five categories - 1.
> unemployed, 2. contributing family workers, own account workers,
> employers, 3. public employees 4. private formal employees 5. informal
> employees.
> I have wage data only for categories 3, 4 and 5. I want to estimate
> wage functions for each of these. As suggested by Rafa de Hoyes in an
> old Statapost (12 April 2006), I defined separate wage variables for
> each of these wage categories.
> w3 is the wage data for public employees. There are 3723 of them.
>
> Now when I run the following model for the public sector, the eventual
> wage equation ends up with only about 400 observations.
>
> selmlog w3 $basefactors1, select(selmcat=$basefactors1 $selfactors) showmlogit
>
> Can somebody please tell me why this is so?
> BTW, I intend bootstrapping to fix the standard errors but will embark
> on that time-consuming exercise once I sort out this problem.
> Thank you in advance,
> Ramani
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-- 
-------------------------------
Joao Ricardo Lima
Professor
UFPB-CCA-DCFS
+553138923914
-------------------------------
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