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From | frone@ria.buffalo.edu |
To | statalist@hsphsun2.harvard.edu |
Subject | Re: st: strata with single sampling units |
Date | Thu, 4 Mar 2010 16:35:55 -0500 |
Steve, Thanks. Yes, it is inappropriate to ignore stratification, but I wasn't sure how to deal with all of the single certainty units.. You mentioned using fpc = 1 for the certainty units. But what about the other units?--no information on the sampling rates. I went back to the various documents for the data and found that they suggested the following code for SUDAAN: PROC procname DESIGN=WR DATA=dsname; NEST stratum psu / MISSUNIT; WEIGHT weight; I haven't seen SUDAAN code in over 15 years, so I'm not sure what MISSUNIT is for. But they aren't using fpc from what I can tell. Then I went back to look at features in -svyset-. An option is singleunit (missing/certainty/scaled/centered). The keyword -certainty- causes strata with single sampling units to be treated as certainty units, thus contributing nothing to the standard error. It seems from the description of the sampling below and your response that using -singleunit (certainty)- would be the way to deal with the single certainty units. So I am now using: svyset psu [pweight=weight], strata(stratum) singleunit(certainty); This works in that I get variance estimates, and they are often much smaller than what one gets ignoring the stratum variable. However, the odd thing is that when I try to replicate their published estimates (proportions) and SEs, I get basically the same SEs if I ignore the stratum variable. The SEs I get using -singleunit (certainty)- tend to be much smaller. Mike Frone sjsamuels@gmail.com Sent by: owner-statalist@hsphsun2.harvard.edu 03/04/2010 02:04 PM Please respond to statalist@hsphsun2.harvard.edu To statalist@hsphsun2.harvard.edu cc Subject Re: st: strata with single sampling units " Would I be safe in assuming that one would use weight and PSU, and ignore strata in this case? " No. Do not ignore the stratum specification. By placing certainty units in their unique strata you ensure that they contribute nothing to the between-PSU component of variance. If the purpose of your study is to describe the population, then the first stage fpc for the certainty units should be 1. Steve Samuels sjsamuels@gmail.com 18 Cantine's Island Saugerties NY 12477 USA 845-246-0774 > When I went back to the documentation it is stated that the study > used a multistage stratified design in which primary sampling units > (PSUs) were stratified according to certain sociodemographic criteria. The > sampling > frame for housing units is the Census 2000/2001 Supplementary Survey > (C2SS) and that > for group quarters is the Census 2000 Group Quarters Inventory. The C2SS > sample of > 655 PSUs was selected at the first stage, including 401 self-representing > (SR) and 254 > non-self-representing (NSR) PSUs. All SR PSUs were selected with > certainty. For the > NSR sample, two PSUs were selected per stratum, with probability > proportional to the > size of the estimated 1996 population of the stratum. NOTE: Sample was > included from each of the 655 PSUs. > However, to prevent potential respondent disclosure, some PSUs were > collapsed so that the final > data file shows 435 PSUs, 305 being SR and 130 being NSR. > > So there are 305 strata with one PSU. Final sample is 43,093. > > Would I be safe in assuming that one would use weight and PSU, and ignore > strata in this case? No other design variables are provided. Doing > things this way seems to replicate SEs in the published tables -- at > least the few I tried to replicate. * * 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/ * * 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/