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| From | Janet Hill <janethill73@yahoo.co.uk> |
| To | "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu> |
| 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 * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/