st: logistic regression complex samples

[Antonio silva <asilva@inbox.com>]

Hello,
I would like to perform binary logistic regression in stratified sampling incorporating 2 variables that represents that design var_weight and var_strata. 
Considering a model with 2 covariates , in SAS I would consider a code like this that works perfectly:

PROC SURVEYLOGISTIC DATA =  dataset
STRATA var_strata;
 
WEIGHT var_weight;
 
 
CLASS covariate1
      Covariate2  ; 
	
MODEL outcome(event='1')= covariate1 covariate2 /clparm vadjust=none ;
  Run;


I tried an equivalent Stata code but does not work. It seems that in Stata its is always necessary have the cluster variable. But in my design I do not have cluster variable,only weight and strata.

svyset [pweight= var_weight], strata(var_strata)  
 
 svy: logistic outcome i.covariate1 i.covariate2

After run , in the output appears only the OR calculated and a note:
Note: missing standard errors because of stratum with single sampling unit.
What is wrong with it?

After that I did some tests considering a fictitious cluster variable and worked.   I suppose this command works only when the 3 design variables weight strata and cluster are used at the same time.

Thanks,
Any help would be much appreciated.
Antonio Silva.

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