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From |
sjsamuels@gmail.com |

To |
"Levinson, Arnold" <Arnold.Levinson@ucdenver.edu> |

Subject |
Re: st: Survey variance estimates - large software differences (resend) |

Date |
Fri, 10 Jul 2009 16:29:47 -0400 |

Arnold, it did appear on June 30 and I replied the first time on July 2nd. Your post had no subject, so it's not obvious on the list; I didn't notice that and so I reply did not have an informative subject. Here's what I responded.. -Steve I cannot tell why the SE's are so different. The n's and outcome means for the subpopulation size total for the "smkskul" are identical in all three analyses, so that is not a problem. I do see some issues. 1. In SAS. the variables in the CLUSTER statement should identify only the PSUs, the 1st stage units. This should, however, lead to smaller, rather than larger standard errors. 2. Stata thinks that there are 46 strata in the entire sample, but SAS thinks that there are 27. SUDAAN and SAS differ by about 1,000 in their report of the sample size for the original population. 3. The subpopulation seems confined to one PSU- one value of "skulid" - and one stratum,, but Stata says that there arere nine PSUs with observations in the subpopulation. Perhaps Stata considers the second stage units,, class rooms, as PSU's in this case, and the othefrs do not. If so, this could account for some of the discrepancy: between-classroom variation could be be small, if there are 16 individuals in nine classrooms. 4. The outcome, according to SUDAAN, is missing for 93% of the subpopulation sample. I suggest that you make sure that variables and observations are identical in the data sets (I notice two different weight variables); make sure that the cluster, classroom, and stratum counts agree in SAS and Stata. Rerun your analyses on this outcome and on one with no missing values and submit your findings to the group with a copy to Jeff Pitblado at Stata. Good luck! Steve * * 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/

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