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From |
sjsamuels@gmail.com |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: interpreting xtmixed results |

Date |
Wed, 26 Aug 2009 14:43:09 -0400 |

Sorry that I'm late in responding to this: You asked about multi-level models vs. survey analysis. "3. I am using xtmixed to analyze a 3-level model (child student district). However, the variance estimates at levels 2 and 3 are almost identical. I would assume this means that I don't need a multilevel model and would be safe in using svyset." Equality of variances at different levels has nothing to do with which levels are needed in a model. If both variances are non-zero, this is definite evidence FOR retaining both levels. Consult a multi-level text to gain a better understanding or talk to a local faculty statistician. Whether you should use the survey analysis or xtmixed depends on your questions of interest. In particular, if it is important to know to quantify the random variation between units at each level, for example, as a way of judging explanatory power of fixed effects at each level, then you should apply the hierarchical model. Also, the mixed model can provide information about random coefficients, not just random intercepts. As to why -svy: reg- was giving you smaller standard errors: you might have unusual data; or perhaps you set up the models incorrectly. It's impossible to tell becaused you did not show us your commands and output (read the FAQ!). . The survey analysis can answer some questions robustly, but not all. Without knowing your study questions, I cannot advise you further. I would present both approaches. Of course, you can have both multi-level models and survey design-based standard errors. In Stata, the -gllamm- command ("findit gllamm") will fit multi-level models with probability weights and clusters. If your school has the HLM software package, the analyses might be e If you wish to estimate the variances on each level, you probably scale the weights. See references in: http://www.stata.com/statalist/archive/2009-07/msg00766.html -Steve -- Steven Samuels sjsamuels@gmail.com 18 Cantine's Island Saugerties NY 12477 USA 845-246-0774 * * 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/

**References**:**st: interpreting xtmixed results***From:*"Tomeka Davis" <soctmd@langate.gsu.edu>

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