Re: st: Re: XTMixed / Repeated Measures

[David Airey <david.airey@vanderbilt.edu>]

I think you have to do something like what has been posted for other  
estimation commands:

http://www.stata.com/statalist/archive/2006-02/msg00060.html

-Dave

On Jan 2, 2009, at 6:43 AM, Paul Bransom wrote:

> David / Maarten,
> Thank you for your assistance. I have a supplementary question.  
> Following anova I often test and adjust for multiple comparisons.  
> With your example:
> . test, test(m1) mtest(sidak)
>
> ( 1)  a[1] - a[2] = 0
> ( 2)  a[1] - a[3] = 0
> ( 3)  a[1] - a[4] = 0
> ( 4)  a[2] - a[3] = 0
> ( 5)  a[2] - a[4] = 0
> ( 6)  a[3] - a[4] = 0
>       Constraint 3 dropped
>       Constraint 4 dropped
>       Constraint 5 dropped
>
> ---------------------------------------
>       |    F(df,21)     df       p
> -------+-------------------------------
>  (1)  |        0.71      1     0.9571 #
>  (2)  |        4.45      1     0.2513 #
>  (3)  |       30.08      1     0.0001 #
>  (4)  |        1.60      1     0.7740 #
>  (5)  |       21.53      1     0.0008 #
>  (6)  |       11.39      1     0.0170 #
> -------+-------------------------------
>  all  |       11.63      3     0.0001
> ---------------------------------------
>              # Sidak adjusted p-values
>
> Is this possible to do after xtmixed as there is no design matrix?
> Thanks.
> Paul
>
>
>
>
> --- On Wed, 31/12/08, David Airey <david.airey@Vanderbilt.Edu> wrote:
>
> > From: David Airey <david.airey@Vanderbilt.Edu>
> > Subject: Re: st: Re: XTMixed / Repeated Measures
> > To: statalist@hsphsun2.harvard.edu
> > Date: Wednesday, 31 December, 2008, 3:44 PM
> > use http://www.ats.ucla.edu/stat/stata/examples/kirk/rb4,
> > clear
> > anova y a s, repeated(a)
> > test _coef[a[3]] = _coef[a[4]]
> > anova, regress // note a[4] was dropped
> > xi: xtmixed y i.a || s: // note a[1] was dropped
> > test _Ia_3 = _Ia_4
> > display r(chi2)/r(df) // scale to show F the same, but here
> > df 1
> >
> > ...shows the same results, yes, and wrt your question, the
> > coefficients shown are relative to the dropped group, in
> > this model. You can also change which group gets dropped.
> >
> >
> >
> >
> >
> > On Dec 31, 2008, at 8:37 AM, Paul Bransom wrote:
> >
> > > Sorry - forgot the subject on my earlier posting
> > >
> > > Hello,
> > > I am trying to teach myself how to use xtmixed for
> > repeated measures anova. Using anova:
> > > anova m method id,repeated(method)
> > > I have a significant effect of method and I can
> > compare the methods:
> > > test _coef[method[1]] = _coef[method[2]]  ( 1)
> > method[1] - method[2] = 0
> > >      F(  1,    27) =   58.27
> > >           Prob > F =    0.0000
> > >
> > > However when I use xtmixed
> > > xi:xtmixed m i.method || id:
> > >
> > > -----
> > ------------------------------------------------------------------------------
> > >          m |      Coef.   Std. Err.      z
> > P>|z|     [95% Conf. Interval]
> > >
> > ------------- 
> > +----------------------------------------------------------
> > > -------------+------
> > > _Imethod_2 |      -12.6   1.650589    -7.63   0.000
> >  -15.8351   -9.364905
> > > _Imethod_3 |      -15.1   1.650589    -9.15   0.000
> >  -18.3351    -11.8649
> > > _Imethod_4 |      -11.1   1.650589    -6.72   0.000
> >  -14.3351   -7.864905
> > >      _cons |       38.6   2.253023    17.13   0.000
> >  34.18416    43.01584
> > > I can again compare all the methods:
> > >
> > > . test _Imethod_2  = _Imethod_3
> > >
> > > with the exception of method 1 as _Imethod_ is the
> > "reference" in the equation.
> > > My question is - how can I compare the effect of
> > method 1 to the other methods or is the fact that these
> > coefficients have a significant p value sufficient (or am I
> > missing something that is so obvious)?
> > > I am using Stata 10.
> > > Thanks,
> > > Paul
> > >
> > >
> > >
> > >
> > >
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