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From |
"Sayer, Bryan" <BSayer@s-3.com> |

To |
"'statalist@hsphsun2.harvard.edu'" <statalist@hsphsun2.harvard.edu> |

Subject |
st: RE: conditional estimates for survey data |

Date |
Fri, 25 Oct 2002 10:49:57 -0400 |

It is hard to generalize about the difference between the conditional and unconditional estimates of the variances. It depends on the within stratum effects. If your population of interest happens to be a subset defined by the stratification variable, you can get away with the conditional (the estimates are actually stratum specific, and then combined). Why would you need to adjust the weights of a sub-pop? And what survey are you using that has 7.5 million observations? If at all possible, I would suggest limiting the number of variables in your file and trying to maintain the full sampling structure. Bryan Sayer Statistician, SSS Inc. bsayer@s-3.com -----Original Message----- From: rpietro@duke.edu [mailto:rpietro@duke.edu] Sent: Thursday, October 24, 2002 2:39 PM To: statalist@hsphsun2.harvard.edu Subject: st: conditional estimates for survey data Hi, I am analyzing a data set containing national survey data with over 7.5 million observations. According to the Stata manual and Cochran's book on sampling, I should use my entire data set to obtain unconditional estimates for the standard error. Any spliting, including the use of commands such as "if", would generate conditional estimates. Given that running the analysis with over 7.5 million observations seems to be computationally challenging, I am now trying to understand the meaning of the conditional estimates I would obtain by restricting my population only to the ones with the condition of interest. Here are my questions to the list: 1. How do I interpret conditional estimates of standard error? Are they generalizable to the target population (individuals with the condition of interest in the entire country)? 2. Would these estimates be smaller than the ones obtained if it were possible to make the estimates based on the entire patient population? 3. Is a conditional standard error necessarily biased in comparison to the unconditional? 4. Can weights be adjusted for a given subpopulation? If so, I would appreciate any references on the subject. many thanks, Rick Ricardo Pietrobon, MD Duke University Medical Center * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/ * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

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