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st: Re: XTMixed / Repeated Measures


From   Paul Bransom <paulbransom@rocketmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: Re: XTMixed / Repeated Measures
Date   Wed, 31 Dec 2008 06:37:08 -0800 (PST)

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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