| Re: Correct use of weights for subsamples [message #28155 is a reply to message #28127] |
Mon, 20 November 2023 08:08   |
Bridgette-DHS
Messages: 3199
Registered: February 2013
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Senior Member |
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Following is a response from Senior DHS staff member, Tom Pullum:
The sampling weight coded in the data files is a characteristic of the cases. It is proportional to the inverse of the sampling fraction. The sampling fraction varies according to the survey design, mainly from one stratum (v023) to another, although it includes a small adjustment for nonresponse. Stratum and nonresponse are the only sources of variation in the weights. Weights do not vary by covariates and do not need to be adjusted if you select sub populations. (If your selection involved subsampling with different sampling fractions for different subpopulations, then an adjustment would be required, but I don't think that's ever done.)
Except for the factor of 1,000,000, the weighted and unweighted numbers of cases in a subpopulation is about the same, but never exactly the same, and such differences are not a problem. The purpose of the weights is to adjust the sample so that estimates of means, proportions, etc., are unbiased, and this requires weighting up or weighting down, depending on whether a stratum was under-sampled or over-sampled.
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