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Weighting between DHS and non DHS surveys [message #16446] Wed, 16 January 2019 04:38 Go to next message
Benjaminnk is currently offline  Benjaminnk
Messages: 2
Registered: January 2019
Member
Hello,

I am working to merge Zambia DHS and a non-DHS survey data related to family planning methods. I want to compare trends in family planning, but the sampling and weighting between the two data sets are different. Do you have any tips for merging and comparing the two data files?
Re: Weighting between DHS and non DHS surveys [message #16449 is a reply to message #16446] Thu, 17 January 2019 08:40 Go to previous messageGo to next message
Bridgette-DHS is currently offline  Bridgette-DHS
Messages: 2548
Registered: February 2013
Senior Member
Please see the following response from Senior DHS Stata Specialist, Tom Pullum:

This is not a situation in which you would merge the files. The term "merge" refers to combining two data files case-by-case. An example would be constructing a file of couples by pairing the data for a man and the data for a woman in the same household into a single line of data. (Such a merge requires using the line numbers of partners, as well as household id code.) In that situation you have a weight for the woman (v005) and a weight for the man (mv005) and you DO have to worry about what the weight should be for the couple. (In that situation we recommend mv005, because nonresponse for men is more serious than women; Stan Becker recommends constructing a "couples weight" in a recent article in the journal Demography.) In your situation, however, you would not do a merge and this is not an issue. For the DHS survey, use the DHS weights; for the other survey, use its weights, if any.


Re: Weighting between DHS and non DHS surveys [message #16556 is a reply to message #16449] Thu, 24 January 2019 03:11 Go to previous messageGo to next message
Benjaminnk is currently offline  Benjaminnk
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Registered: January 2019
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Thank you for the response Tom. I misspoke and the term I meant to use was "amend". Would you suggest that I follow the same procedure that you outlined above to amend the files?
Re: Weighting between DHS and non DHS surveys [message #16557 is a reply to message #16556] Thu, 24 January 2019 08:44 Go to previous message
Bridgette-DHS is currently offline  Bridgette-DHS
Messages: 2548
Registered: February 2013
Senior Member

Please see the following response from Senior DHS Stata Specialist, Tom Pullum:

Benjamin--I think the word you are looking for is "append". That's when two files are combined into one file by, basically, stacking them. If one file has 10,000 cases and the other has 5,000 cases, then the combined file has 15,000 cases. This can be done when working with two DHS surveys, say, because both surveys will have almost exactly the same variable names and categories of variables. For example, when appending two IR files, v013 will be age in five-year intervals in both surveys. But if you have a DHS survey and a non-DHS survey, with different variable names and potentially different categories of variables, then appending will only be useful if you rename and recode the variables in one survey to match the other survey. That's what you would have to do, if the second survey was a MICS survey, for example, because MICS uses different variable names.

Perhaps you want to do this so you can pool the two surveys and get an estimate of something that draws from both surveys. I personally would avoid doing this (but there's no law against it...). The two surveys probably refer to different dates, and the reference time for any estimates will be blurred. From a statistical perspective, a pooled estimate should weight the surveys in proportion to their size. For example, if E1 and E2 are the estimates from the two surveys, and the surveys have N1 and N2 cases, respectively, then the pooled estimate would be E=(N1*E1 + N2*E2)/(N1+N2) . But if E1 and E2 are different, especially if they are statistically significantly different, then I'd prefer just to report E1 and E2 and not calculate the pooled estimate E.
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