Home » Data » Weighting data » Interpretation of Rescaled household level weights for IndiaNFHS4 (rescaling household level weights for multinomial logit regression and interpretation)
Interpretation of Rescaled household level weights for IndiaNFHS4 [message #18651] 
Mon, 20 January 2020 11:28 
preshit
Messages: 13 Registered: March 2018 Location: Tucson, AZ, USA

Member 


Hello DHS Forum Members,
My apologies in advance for lengthy post but I want to explain the issue in detail so it will be useful to others as well. For my analysis, I am using the NFHS4 PR file and multinomial logit regression. I am stratifying my analysis on rural and urban samples and using svy command for populationlevel inference. I have rescaled my weight variable and my Stata code looks like below:
gen newhv005= hv005/1000000
svyset,clear
svyset [pw=newhv005],psu(hv021)strata(hv023) singleunit(centered)
svy, subpop(if respondent_residence==0) : mlogit Y X1##(i.X2 i.X3) i.X4 i.X5 i.State Fixed Effect // for rural sample
mlogit,rrr
svy, subpop(if respondent_residence==1) : mlogit Y X1##(i.X2 i.X3) i.X4 i.X5 i.State Fixed Effect // for urban sample
mlogit,rrr
svy : mlogit Y X1##(i.X2 i.X3) i.X4 i.X5 i.respondent_residence i.State Fixed Effect // for entire sample
mlogit,rrr
I have tested my code with and without svy setting my data. Without svyset all mlogit regressions give me coefficients, SEs, CIs, and associated Pvalues. However, when I svyset my data, for urban sample, I am getting the following error:
Warning: variance matrix is nonsymmetric or highly singular
And the output is missing SEs, CIs, and associated Pvalues.
I searched the Stata user forum and realized this error is because one of my Strata has only one PSU which can be checked with the command:
svydes if respondent_residence==1 //to check if there is only one PSU within any strata
I approached Stata Technical Support and received the following reply:
I have checked your data, the pweight you are using, newhv005, has a
relatively big variation. The minimum value is .000673 and the maximum
is 38.9548. If the computation has perfect precision, there will not be
a problem. However, all the computation on computers have limited
precision, and mlogit is particularly sensitive to variation in
pweight. The missing value you saw is a numerical problem because of
limited precision. You should check your data to see why the pweight has
such a big variation.
If you still want to use the same pweight variable, you can avoid this
numerical problem by rescaling your pweight. Instead of dividing hv005
by 1000000, you can divide it by 100000000 or larger number. This will
solve the problem of missing SE. Please note that rescaling the pweight
does not affect the point estimates or standard errors of the
coefficients. It only affects the population size reported. In this
case, you should use a different unit to interpret the population size
reported, e.g., instead of using one person, you should use a group of
100 persons as the unit.
*********
Given this reply I have the following questions:
1. How the interpretation of mlogit will change if I rescale pweight to 10000000 and not to the recommended 1million?
2. Or shall I rescale the pweight in some other way?
3. Is there any other way I should specify my model?
Thank you in advance for your time and for reading the post.
Regards
Preshit



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