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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   Sun, 20 Apr 2008 03:23:46 -0300

Ramani,

sorry but I can't help you. With me the selmlog works well. Send a
mail to Rafa - rdehoyos@worldbank.org.

Best,

Joao Ricardo Lima



2008/4/20, Ramani Gunatilaka <ramani.gunatilaka@gmail.com>:
> Dear Joao Lima,
> Thank you for your response. Sample size by select_m depvar category
> is as follows, there are no missing values:
> tabulate selmcat
>
> categorical
> variable
> showing
> employment
> sector
> choice       Freq.      Percent Cum.
>
> 1       1,884   6.36    6.36
> 2      12,238   41.34   47.70
> 3       3,723   12.58   60.28
> 4       5,043   17.03   77.31
> 5       6,716   22.69   100.00
>
> Total      29,604       100.00
>
> . sum w3
>
> Variable        Obs     Mean    Std. Dev.       Min     Max
>
> w3       3723   4.013316        1.095727        -6.050407       6.69982
>
> Public sector wage variable W3 has values for all 3723 public employee
> observations and missing values for the observations relating to other
> employment categories.
>
> . sum $basefactors1
>
> Variable        Obs     Mean    Std. Dev.       Min     Max
>
> male      29604 .6367721        .4809379        0       1
> age      29604  38.82702        13.52627        11      93
> agesqd      29604       1690.491        1133.976        121     8649
> SL_Tamil      29604     .042832 .2024817        0       1
> I_Tamil      29604      .056614 .2311074        0       1
>
> Moor      29604 .0472571        .2121919        0       1
> other      29604        .0040873        .0638022        0       1
> jsecondary      29604   .2399676        .4270706        0       1
> ssecondary      29604   .5070599        .4999586        0       1
> tertiary      29604     .0330699        .178822 0       1
>
> managerial      29604   .0839751        .2773552        0       1
> professional      29604.0482029 .2141984        0       1
> technician      29604   .0463789        .2103078        0       1
> clerical      29604     .0352317        .1843681        0       1
> service      29604      .0671869        .2503496        0       1
>
> agricultural      29604 .2110526        .4080625        0       1
> elementary      29604   .2822929        .4501227        0       1
> manuf      29604        .2341913        .4234995        0       1
> services      29604     .3759627        .4843786        0       1
> rural      29604        .8120524        .3906769        0       1
>
> estates      29604      .0733685        .2607448        0       1
> CP      29604   .1397784        .3467628        0       1
> SP      29604   .1732874        .3785019        0       1
> NWP      29604  .1327523        .3393126        0       1
> NCP      29604  .0744494        .2625053        0       1
>
> Uva      29604  .0816444        .2738268        0       1
> Sab      29604  .118261 .3229224        0       1
>
> I don't have any missing values for $basefactors1 variables - almost
> all are 0/1 dummies.
>
> . sum $selfactors
>
> Variable        Obs     Mean    Std. Dev.       Min     Max
>
> nempld  29604   2.234901        1.141517        0       9
> nempld_m        29604   5.670382        5.652145        0       54
> children        29604   .6210985        .8557174        0       6
> mother  29604   .140758 .3477776        0       1
> hh_head 29604   .4264626        .494571 0       1
>
> married 29604   .6940616        .4608115        0       1
> malemarried     29604   .4621673        .4985751        0       1
>
> There are no missing values for the demographic variables used for the
> selection equation.
>
> Thank you for your help.
> Best,
> Ramani
>
>
> On 19/04/2008, Joao Ricardo F. Lima <jricardofl@gmail.com> wrote:
> > 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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> >
> *
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>


-- 
-------------------------------
Joao Ricardo Lima
Professor
UFPB-CCA-DCFS
+553138923914
-------------------------------
*
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