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Re: Using weights in regression analysis [message #850 is a reply to message #848] Sun, 20 October 2013 19:09
 Reduced-For(u)m Messages: 292Registered: March 2013 Senior Member

Here is some discussion of the problem, which continues in more (and helpful) detail if you follow the link.

http://www.stata.com/support/faqs/statistics/stratum-with-on e-psu/

Having a stratum with a single PSU is a fairly common problem. When there is only one PSU within a stratum, there is insufficient information with which to compute an estimate of that stratum's variance. Therefore, it is impossible to compute the variance of an estimated parameter when the data are from a stratified clustered design. There are two solutions. The first solution is to simply delete the stratum with the singleton PSU from your sample. The second solution is to treat the data from that stratum as though it is from another stratum. In order to implement either solution, one must first identify which strata are affected and which observations in the dataset belong to those strata. The svydes command will identify the strata with singleton PSUs by placing an asterisk next to the stratum identifier. For example, in the output below, stratum 1 is identified as having only 1 PSU.

The other possibility (I think) is to use the subpop command, which is discussed in another context here:
http://www.icpsr.umich.edu/icpsrweb/CPES/support/faqs/2011/0 4/how-should-i-detect-and-handle-single

I really wish I understood better what kind of estimator this particular "svy" command is using, but I've still not found good documentation describing it, so I can't explain exactly why this is a problem in a mathematical/statistical sense. One other thing people have worried about here is the weighting - since you are only using people who have tested positive for HIV, you are pretending like HIV + is orthogonal to sampling probability, and I'm pretty sure it wouldn't be (because HIV is not distributed randomly across geography and SES class). But I wouldn't think it makes that much difference.

One alternative strategy would be just to give up on the weights and cluster at some larger-than-PSU geographic level - say maybe region if there are many regions (if there are few regions, the wild-t bootstrap would work and I would think you would "cluster" those by strata, because I'm guess that is something like region-by-urban status). Something like:

logistic unmetneed i.v106 if hivtest_result ==1, cluster(region)

Let me know if this helps.

 Using weights in regression analysis By: DHS user on Wed, 20 February 2013 11:48 Re: Using weights in regression analysis By: Bridgette-DHS on Wed, 20 February 2013 11:50 Re: Using weights in regression analysis By: enuanand on Tue, 19 March 2013 23:32 Re: Using weights in regression analysis By: Fabrice LOTY on Wed, 20 March 2013 05:34 Re: Using weights in regression analysis By: Traore on Wed, 20 March 2013 03:54 Re: Using weights in regression analysis By: Trevor-DHS on Wed, 20 March 2013 20:17 Re: Using weights in regression analysis By: idas on Fri, 29 March 2013 13:59 Re: Using weights in regression analysis By: Reduced-For(u)m on Sat, 30 March 2013 19:14 Re: Using weights in regression analysis By: idas on Tue, 02 April 2013 13:15 Re: Using weights in regression analysis By: Bridgette-DHS on Thu, 11 April 2013 17:31 Re: Using weights in regression analysis By: mnicolson on Fri, 14 June 2013 16:18 Re: Using weights in regression analysis By: Reduced-For(u)m on Fri, 14 June 2013 17:24 Re: Using weights in regression analysis By: smgwu on Thu, 17 October 2013 20:19 Re: Using weights in regression analysis By: Reduced-For(u)m on Sun, 20 October 2013 19:09 Re: Using weights in regression analysis By: myigzaw on Tue, 16 April 2013 08:25 Re: Using weights in regression analysis By: Reduced-For(u)m on Fri, 19 April 2013 01:04 Re: Using weights in regression analysis By: Bridgette-DHS on Fri, 26 April 2013 10:48 Re: Using weights in regression analysis By: Khaing Zar on Sat, 22 September 2018 02:31 Re: Using weights in regression analysis By: Bridgette-DHS on Mon, 24 September 2018 09:16 Re: Using weights in regression analysis By: kindu on Sat, 25 January 2020 12:09 Re: Using weights in regression analysis By: soumava on Wed, 07 February 2018 16:49 Re: Using weights in regression analysis By: Bridgette-DHS on Thu, 08 February 2018 09:40 Re: Using weights in regression analysis By: Khaing Zar on Thu, 20 September 2018 21:14
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