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re: st: Stumped...xtmixed and ANOVA F-stats not agreeing for balanced design


From   "Airey, David C" <david.airey@vanderbilt.edu>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   re: st: Stumped...xtmixed and ANOVA F-stats not agreeing for balanced design
Date   Thu, 5 May 2011 08:04:25 -0500

.

> Dear all,
> 
> Thanks for all the help in previous messages. This thoughtful user community makes learning all the more enjoyable, so  thank you.
> 
> Hope some of the experts out there can help me  get passed a stumping issue, comparing xtmixed with ANOVA.
> 
> I'm running a Within-Subject model with 2 factors (a, b). The F-stats produced by the two methods are not agreeing, despite having balanced data.

Some of the random effects look to be very small, indicating poor fit? So is the ANOVA well fit, and meeting the required assumptions? This may not be the case for repeated measures univariate ANOVA with regard to sphericity. It seems to me that ANOVA in Stata will spit out an answer when xtmixed will choke, when xtmixed should indeed choke. I think maybe we should qualify getting the same results between the two methods for well fit, balanced models? Anyway, tell us if you think both models are well fit.



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