st: margins with svy: biprobit

[Wassim Tarraf <tarrafwassim@gmail.com>]

Dear list members- I am estimating a bivariate probit model (with svy: 
biprobit; as per the example code below) in Stata 11.1 using complex 
design survey data. Using the margins command while specifying the 
subpopulation used to estimate the model and the vce(unconditional) 
option leads to Stata issuing the following error message : 
"unconditional standard errors derived assuming full estimation sample; 
indepvars dropped observations from the estimation sample." I am faced 
with the same problem when estimating a single equation probit (or 
logit) as well. Any clarification on what the problem might be would be 
greatly appreciated.

****begin code********************************
svyset  cluster [pweight=weight], strata(strata)
svy, subpop(if a==1 & b==2): biprobit x1 x2 i.y1 i.y2 i.y3
margins i.y1, subpop(if a==1 & b==2) vce(unconditional)
****end code*********************************

Thanks,
Wassim

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