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Re: st: Complex survey with only sampling weights


From   "Michael I. Lichter" <MLichter@Buffalo.EDU>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Complex survey with only sampling weights
Date   Fri, 29 May 2009 09:54:14 -0400

The study description suggests that this is a complex probability sample, but by failing to provide you with identifiers for the strata, PSUs, and secondary sampling units, the original researchers made it impossible for you to estimate the effects of stratification and clustering. This is a problem, whether the sample was a true probability sample or not; your standard errors will almost certainly be too small regardless of how you calculate them.

The "sampling weights" appear to be poststratification weights based on external (census or other) estimates of true population values, rather than design-based probability weights. You can treat them as either pweights in "regular" Stata commands or as poststratification weights in -svy- commands and I think you will get the same answers either way, although if you use them as poststratification weights, you have to be more careful about subsetting.

In any event, Ana is right; the failure of the researchers to give you enough information about the design and the weights is not a rationale for ignoring the weights, especially for simple tabulations.

Michael

Ana Gabriela Guerrero Serdan wrote:
the survey you describe is complex but it doesnt mean that is not random. Its just that to save costs or to be sure that they do include specific groups/workers they have done stratification and clustering. You probably need to use svy commands in Stata. But his depends on what you are intersting on estimating, for population totals and descriptives you certainly would need. SPSS version 12 has a complex samples options, so you would be able to get this also in SPSS. see svy commands in Stata take a look at Cameron and Trivedi, microeconometricts,chapter on stratified and cluster samples. rgds, Gaby

--- On Fri, 5/29/09, [ISO-8859-1] Fernando Terrés <fernando.terres@upc.edu> wrote:

From: [ISO-8859-1] Fernando Terrés <fernando.terres@upc.edu>
Subject: st: Complex survey with only sampling weights
To: statalist@hsphsun2.harvard.edu
Date: Friday, May 29, 2009, 5:50 AM
I need to analyze an official survey,
with data on 11,054 workers, were the sampling design is according to the survey company: 'multistage, stratified by clusters, with random selection of both PSU (602 undisclosed municipalities), and secondary sampling units (undisclosed census sections), and the last sample units (workers) are selected by random routes and quotes'. They provide sampling weights that are (1681) unique values for each combination of gender (2), region (17), firm size (6), and economic activity (13).
My question is very simple: is this a probabilistic
sampling design? I suspect that it is not, but I cast some doubts because the documentation disclosed by the official bureau that commissioned the survey clearly insists on using the weights (they present a word document tabulating them), that are the only sampling information included in the SPSS files that they provide (this reinforces my doubts, because I'm using Stata 10, which correctly uses the sampling weights, while to my knowledge SPSS only uses frequency weights).
Thank you in advance,
Fernando.

--
Fernando Terres
Lecturer. PhD candidate
CERPIE/Research
Universitat Politecnica de Catalunya
Diagonal, 647 - 10
08028 Barcelona (Spain)
+34.934.010.708
fernando.terres@upc.edu
http://cerpie.upc.edu


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--
Michael I. Lichter, Ph.D. <mlichter@buffalo.edu>
Research Assistant Professor & NRSA Fellow
UB Department of Family Medicine / Primary Care Research Institute
UB Clinical Center, 462 Grider Street, Buffalo, NY 14215
Office: CC 125 / Phone: 716-898-4751 / FAX: 716-898-3536

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