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From |
"Ridolfo, Heather E. (CDC/CCHIS/NCHS) (CTR)" <evd7@CDC.GOV> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
st: Svy mean using subpop and incorrect number of observations |

Date |
Wed, 23 Jul 2008 11:14:26 -0400 |

All, I recently posted a question regarding losing observations and PSUs when using svy regress and the subpop command. Jeff Pitblado recommended I update the version of stata I was using to correct this problem. "Heather should check that her Stata is fully up-to-date. On 02apr2008, we posted an ado-file update that fixed a problem similar to what Heather is describing above. Here is the corresponding entry from -help whatsnew-: 5. svy's linearized variance estimator was marking out observations that had missing values in the independent variables for observations outside the subpopulation. This affects the estimated variance values when the primary sampling units were the individual observations and could decrease the design degrees of freedom. Both of these effects are very slight and inversely related to the sample size. This has been fixed. Note that, prior to this update, entire PSU's can be dropped if each observation within the PSU contains a missing value in one of the variables in the model fit. With an updated Stata, only observations containing missing values within the subpop are dropped." This did in fact fix the problem. However, I am still having a problem when I run svy, mean. svyset psuscid [pweight = gswgt1], strata(region) svy, subpop(bhgsp): mean efficacy esteem child_sex age meduc new_inc2 dm_support dm_college m_indep MDCOLLEG md_spprt MDACHIEV, over(racebh) Survey: Mean estimation Number of strata = 4 Number of obs = 4657 Number of PSUs = 121 Population size = 3921354 Subpop. no. obs = 2126 Subpop. size = 1736680 Design df = 117 If STATA is dropping observations from my original dataset due to incomplete data, is the survey design information from these observations retained in the calculation of the standard errors? Is there any way to fix this or another way to get means while using the survey commands and subpop? Thanks, Heather * * 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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