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st: Re: pwcompare
From
Janet Hill <[email protected]>
To
"[email protected]" <[email protected]>
Subject
st: Re: pwcompare
Date
Fri, 25 Nov 2011 16:35:40 +0000 (GMT)
Why does pwcompare give different results after anova and xtmixed? Using the following syntax:
xtmixed lhist i.group##i.time || dog:, reml cov(id)
or
anova lhist group / dog|group time time#group, repeated(time)
followed by
pwcompare group, emptycells(reweigh) eff asbalanced post
I get the following for xtmixed
------------------------------------------------------------------------------
| Unadjusted Unadjusted
| Contrast Std. Err. z P>|z| [95% Conf. Interval]
-------------+----------------------------------------------------------------
lhist |
group |
2 vs 1 | -.4591643 .5681373 -0.81 0.419 -1.572693 .6543643
3 vs 1 | 1.200595 .525993 2.28 0.022 .1696677 2.231522
4 vs 1 | -.3857097 .525993 -0.73 0.463 -1.416637 .6452175
3 vs 2 | 1.659759 .5681373 2.92 0.003 .5462306 2.773288
4 vs 2 | .0734546 .5681373 0.13 0.897 -1.040074 1.186983
4 vs 3 | -1.586305 .525993 -3.02 0.003 -2.617232 -.5553775
------------------------------------------------------------------------------
and for the anova
------------------------------------------------------------------------------
| Unadjusted Unadjusted
| Contrast Std. Err. t P>|t| [95% Conf. Interval]
-------------+----------------------------------------------------------------
group |
2 vs 1 | -.4591643 .1047385 -4.38 0.000 -.6722564 -.2460723
3 vs 1 | 1.200595 .096969 12.38 0.000 1.00331 1.39788
4 vs 1 | -.3857097 .096969 -3.98 0.000 -.5829947 -.1884248
3 vs 2 | 1.659759 .1047385 15.85 0.000 1.446667 1.872851
4 vs 2 | .0734546 .1047385 0.70 0.488 -.1396375 .2865467
4 vs 3 | -1.586305 .096969 -16.36 0.000 -1.78359 -1.38902
------------------------------------------------------------------------------
I can see that the standard errors are different, but the question arises should I use xtmixed or anova for repeated measures?
I am using Stata 12.0, update 10 Nov 2011.
Thanks,
Janet
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