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Re: st: test after margins and xtmixed


From   Ricardo Ovaldia <ovaldia@yahoo.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: test after margins and xtmixed
Date   Mon, 12 Mar 2012 08:31:10 -0700 (PDT)

Ooops, I am sorry. I meant:

. test 1.group#3.month= 2.group#3.month= 3.group#3.month

 ( 1)  1bn.group#3bn.month - 2.group#3bn.month = 0
 ( 2)  1bn.group#3bn.month - 3.group#3bn.month = 0

           chi2(  2) =   12.22
         Prob > chi2 =    0.0022





Ricardo Ovaldia, MS
Statistician 
Oklahoma City, OK


--- On Mon, 3/12/12, Austin Nichols <austinnichols@gmail.com> wrote:

> From: Austin Nichols <austinnichols@gmail.com>
> Subject: Re: st: test after margins and xtmixed
> To: statalist@hsphsun2.harvard.edu
> Date: Monday, March 12, 2012, 9:50 AM
> Ricardo Ovaldia <ovaldia@yahoo.com>:
> You are testing whether the sixes are equal to zero, not
> whether the
> sixes are equal to each other.
> 
> On Mon, Mar 12, 2012 at 10:46 AM, Ricardo Ovaldia <ovaldia@yahoo.com>
> wrote:
> > Dear all,
> >
> > I have a question about using –margins- and –test-
> after –xtmixed- to test if “groups” differ at specific
> times. I am concerned with the small SE that margin
> reports.
> >
> > Here is an example:
> >
> > I fit the following -xtmixed- model:
> > . xtmixed ft i.group##month || id: group,
> cov(unstructured) mle
> >
> > And I am interested in comparing the group effect at
> certain time, 3 months for example, I used –margins, post-
> and then –test-:
> >
> > . margins, over(group month) post
> >
> > Predictive margins                        
>        Number of obs   =        344
> >
> > Expression   : Linear prediction, fixed portion,
> predict()
> > over         : group month
> >
> >
> >
> ------------------------------------------------------------------------------
> >             |            Delta-method
> >             |     Margin   Std. Err.      z
>    P>|z|     [95% Conf. Interval]
> >
> -------------+----------------------------------------------------------------
> >  group#month |
> >       1  3  |   6.382194   .0760204    83.95
>   0.000     6.233196    6.531191
> >       1  6  |   7.693377   .0819562    93.87
>   0.000     7.532746    7.854008
> >       1  9  |   8.709543   .1006514    86.53
>   0.000      8.51227    8.906816
> >       1 12  |   9.167792   .1323406    69.27  
> 0.000     8.908409    9.427175
> >       2  3  |   6.053284   .0700887    86.37
>   0.000     5.915913    6.190655
> >       2  6  |   7.900573   .0777758   101.58  
> 0.000     7.748135    8.053011
> >       2  9  |   9.124052   .1023024    89.19
>   0.000     8.923543    9.324561
> >       2 12  |   10.04959   .1374368    73.12  
> 0.000     9.780223    10.31897
> >       3  3  |   6.074073   .0780239    77.85
>   0.000     5.921149    6.226997
> >       3  6  |   7.949809   .0856802    92.78
>   0.000     7.781879    8.117739
> >       3  9  |   9.337498   .1128377    82.75
>   0.000      9.11634    9.558655
> >       3 12  |   10.14703   .1480792    68.52  
> 0.000     9.856798    10.43726
> >
> ------------------------------------------------------------------------------
> >
> > . test 1.group#3.month 2.group#3.month 3.group#3.month
> >
> >  ( 1)  1bn.group#3bn.month = 0
> >  ( 2)  2.group#3bn.month = 0
> >  ( 3)  3.group#3bn.month = 0
> >
> >           chi2(  3) =19762.54
> >         Prob > chi2 =    0.0000
> >
> > Is this correct?
> 
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