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Re: st: margins after logit model


From   Tirthankar Chakravarty <tirthankar.chakravarty@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: margins after logit model
Date   Wed, 29 Dec 2010 15:42:46 -0800

One way to do this is to re-estimate with the group you want omitted
set as the base group in the logit regression:

*****************************************
webuse lbw, clear
logit low age lwt i.race smoke ptl ht ui
margins, dydx(race)
logit low age lwt b2.race smoke ptl ht ui
margins, dydx(race)
*****************************************

T

On Wed, Dec 29, 2010 at 3:36 PM, Haiyong Xu <hxu@mednet.ucla.edu> wrote:
>
> Hi,
> Wish you all have wonderful holidays!
>
> My logit model and the output are as follows:
>
> logit psydrgnobzn i.female age i.year, vce(cluster cluster_id)
>
> Logistic regression                               Number of obs   =
> 40284
>                                                 Wald chi2(4)    =
> 422.81
>                                                 Prob > chi2     =
> 0.0000
> Log pseudolikelihood = -26350.649                 Pseudo R2       =
> 0.0127
>
>                        (Std. Err. adjusted for 13428 clusters in
> cluster_id)
> ------------------------------------------------------------------------------
>            |               Robust
> psydrgnobzn |      Coef.   Std. Err.      z    P>|z|     [95% Conf.
> Interval]
> -------------+----------------------------------------------------------------
>   1.female |   .5114119   .0357798    14.29   0.000     .4412848
> .5815389
>        age |  -.0191765   .0023834    -8.05
> 0.000    -.0238479   -.0145051
>            |
>       year |
>      2006  |    .154101   .0147308    10.46   0.000     .1252292
> .1829728
>      2007  |   .2495566   .0171274    14.57   0.000     .2159875
> .2831257
>            |
>      _cons |   .5000495   .1866511     2.68   0.007       .13422
> .865879
> ------------------------------------------------------------------------------
>
> After the logit model, I run margins command to get the marginal effect.
> . margins, dydx(year)
>
> Average marginal effects                          Number of obs   =
> 40284
> Model VCE    : Robust
>
> Expression   : Pr(psydrgnobzn), predict()
> dy/dx w.r.t. : 2006.year 2007.year
>
> ------------------------------------------------------------------------------
>            |            Delta-method
>            |      dy/dx   Std. Err.      z    P>|z|     [95% Conf.
> Interval]
> -------------+----------------------------------------------------------------
>       year |
>      2006  |   .0351202   .0033485    10.49   0.000     .0285573
> .0416832
>      2007  |   .0575292   .0039259    14.65   0.000     .0498345
> .0652239
> ------------------------------------------------------------------------------
> Note: dy/dx for factor levels is the discrete change from the base level.
>
> The year variables has three values 2005, 2006 and 2007. Stata automatically
> set 2005 as the omit group. I wonder if I can set 2006 as the reference
> group so that I can get the margin effect between 2006 and 2007.
>
> Thanks.
> Haiyong
>
>
>
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>
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To every ω-consistent recursive class κ of formulae there correspond
recursive class signs r, such that neither v Gen r nor Neg(v Gen r)
belongs to Flg(κ) (where v is the free variable of r).

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