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RE: st: Re: Repeated Measures ANOVA vs. Friedman test


From   "Airey, David C" <david.airey@vanderbilt.edu>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   RE: st: Re: Repeated Measures ANOVA vs. Friedman test
Date   Tue, 22 May 2012 11:07:59 -0500

.

That's true; the contrast postestimation command will use a t after regress/ANOVA but a z after xtmixed. On the other hand, the compound symmetric covariance for regress/ANOVA may not be a good choice, and the univariate corrections for departure from the sphericity assumption are approximate. Also, with other than designed experiments, missing time points are likely, and regress/ANOVA does casewise deletion whereas xtmixed will retain cases missing one time point.

> One more thing - if you can "get away with" the assumptions for ANOVA and everything is balanced, it should provide closer to nominal test levels than -xtmixed- because of the finite degrees of freedom for error in the former vs. asymptotic Z- statistics in the latter.
> 
> Al Feiveson
> 



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