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Re: st: logistic regression complex samples


From   Steve Samuels <sjsamuels@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: logistic regression complex samples
Date   Wed, 7 Dec 2011 17:51:32 -0500

Antonio:

 If Stata says you have a stratum with a single sampling unit, then you do, and this unconnected to whether you specified the PSU in  in -svyset-.  Tabulating the strata should identify the problem.  If you do have  strata with only one observation, how is the program to compute an estimate of variability that includes those observations? That is the subject of the error message. I personally suggest that you merge singleton strata into adjacent ones, but there are other options, including -singleunit- options in -svyset- and others in Korn and Graubard, 1989, Section 5.3.

And please read the Statalist FAQ especially Section 3.3, before posting again.


Steve



Ref: Korn, E. L., & Graubard, B. I. (1999). Analysis of health surveys (Wiley series in probability and statistics). New York: Wiley.




On Dec 7, 2011, at 12:18 PM, Stas Kolenikov wrote:

Antonio,

it would help if you mentioned the version of Stata that you are
using. By default, Stata would use observations as PSUs (and the
output of -svyset- would state that -- again, it would help if you
included the output of both commands). You can also achieve the effect
of specifying observations as PSUs via -svyset _n ...-.

On Wed, Dec 7, 2011 at 10:05 AM, Antonio silva <asilva@inbox.com> wrote:
> 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.

-- 
Stas Kolenikov, also found at http://stas.kolenikov.name
Small print: I use this email account for mailing lists only.

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