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From |
Steve Samuels <sjsamuels@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: can the total sampling weights be applied to subsample analysis |

Date |
Mon, 24 May 2010 16:21:57 -0400 |

No, it just means, if anything, that you should not make much of small differences.. In the admittedly artificial example in L&L's book, the estimate of the subpopulation mean was $11.52, compared to the true value of $11.60. I can think of examples where a difference in the distribution of weights would be expected and would not lead to bias. No sampling text advises against using the sample weights, and I would use them. Note that if a subpopulation size is <20, then the standard errors that Stata reports will be untrustworthy. Steve Steven Samuels sjsamuels@gmail.com 18 Cantine's Island Saugerties NY 12477 USA Voice: 845-246-0774 Fax: 206-202-4783 On Mon, May 24, 2010 at 3:37 PM, <jl591164@albany.edu> wrote: > Thanks, Steve. T-test and ranksum test indicate that the means of the > weights in the subpopulaiton and its complement are significantly > different. Does this mean that it is better not to apply the original > smaple weights to the subsample discriptive analysis? Thanks a lot. > > Junqing > > >> The subpopulation observations receive the original sample weights. >> These might not be appropriate for the subpopulation and can lead to >> bias (See an example in Levy and Lemeshow, Sampling of Populations, >> Wiley, 2008, pp. 147-148). There's not much that you can do about that >> without external information about the subpopulation. I speculate >> (but could be wrong!) that the bias arises when the probability of >> being a subpopulation member is correlated with the original weights. >> If so, you can check for this bias by plotting the subpopulation >> indicator against the weights with -ksm-. Or, more simply, just >> check whether the distributions of the weights in the subpopulation >> and its complement are different, >> >> Steve >> >> Steven Samuels >> sjsamuels@gmail.com >> 18 Cantine's Island >> Saugerties NY 12477 >> USA >> Voice: 845-246-0774 >> Fax: 206-202-4783 >> >> On Fri, May 21, 2010 at 1:40 PM, <jl591164@albany.edu> wrote: >>> Thanks. That is acturally what i did, useing survey set first, then svy, >>> subpop(). The subpop() option will use all cases in the calculation of >>> standard errors, but only the subsample in the calculation of the point >>> estimates. So, the total sampling weights will be used in the caculation >>> of standard errors of subsample. I have a follow up question. How the >>> total weights are applied to point estimates of the subsample by >>> subpop()? >>> >>> >>>> On Fri, May 21, 2010 at 11:32 AM, <jl591164@albany.edu> wrote: >>>>> My data provides a sampling weight to each id. But my study is based >>>>> on >>>>> a >>>>> subsample of the data becasue i selected cases by two variables: age >>>>> and >>>>> type of placement. Can I still apply the whole sample weights to my >>>>> subsample descriptive analysis? Thanks a lot. >>>> >>>> You should use the compete sample with -svy, subpop()- option. See >>>> http://www.stata-journal.com/article.html?article=st0153. -- Steven Samuels sjsamuels@gmail.com 18 Cantine's Island Saugerties NY 12477 USA Voice: 845-246-0774 Fax: 206-202-4783 * * 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**:**Re: st: can the total sampling weights be applied to subsample analysis***From:*jl591164@albany.edu

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