R help - Oct 2005 - "Survey" package and NAMCS data... unsure of specification

Hello, all.

I wanted to use the "survey" package to analyze data from the National
Ambulatory Medical Care Survey, and am having some difficulty translating
the analysis keywords from one package (Stata) to the other (R). The data
were collected using a multistage probability sampling, and there are
variables included to identify the sampling units and weights. Documentation
from the NAMCS describes this for Stata as follows (note the variable names
in the data are in caps):

The pweight (PATWT), strata (CSTRATM), and PSU (CPSUM) are set with the
svyset command as
follows:
svyset pweight PATWT
svyset strata CSTRATM
svyset psu CPSUM


They provide similar instructions for SUDAAN: as
SUDAAN 1-stage WR Option
The program below provides a with replacement ultimate cluster (1-stage)
estimate of standard errors for a
cross-tabulation.
PROC CROSSTAB DATA=COMB1 DESIGN=WR FILETYPE=SAS;
NEST CSTRATM CPSUM/MISSUNIT;

In R, the svydesign command is used to set the sampling scheme, but as
follows (example from the documentation):

dstrat <- svydesign(id=~1,strata=~stype, weights=~pw, data=apistrat,
fpc=~fpc)

 stratified on stype, with sampling weights pw. The fpc variable contains
the population size for the stratum. As the schools are sampled
independently, each record in the data frame is a separate PSU. This is
indicated by id=~1. Since the sampling weights could have been determined
from the population size an equivalent declaration would be

dstrat <- svydesign(id=~1,strata=~stype,  data=apistrat, fpc=~fpc)

I get that the "weights" should be PATWT, and it seems that the
"strata"
should be CSTRATM, but I'm unsure of how to handle the primary sampling
units (CPSUM).

Does anyone have any suggestions?

--
---------------------------------------
David L. Van Brunt, Ph.D.
mailto:dlvanbrunt@gmail.com

	[[alternative HTML version deleted]]

On Tue, 4 Oct 2005, David L. Van Brunt, Ph.D. wrote:
> Hello, all.
>
> I wanted to use the "survey" package to analyze data from the
National
> Ambulatory Medical Care Survey, and am having some difficulty translating
> the analysis keywords from one package (Stata) to the other (R). The data
> were collected using a multistage probability sampling, and there are
> variables included to identify the sampling units and weights.
Documentation
> from the NAMCS describes this for Stata as follows (note the variable names
> in the data are in caps):
>
> The pweight (PATWT), strata (CSTRATM), and PSU (CPSUM) are set with the
> svyset command as
> follows:
> svyset pweight PATWT
> svyset strata CSTRATM
> svyset psu CPSUM
>
Supposing your data frame is called 'namcs'

dnamcs <- svydesign(id=~CPSUM, strata=~CSTRATM, weight=~PATWT, data=namcs)

or perhaps

dnamcs <- svydesign(id=~CPSUM, strata=~CSTRATM, weight=~PATWT,
                       data=namcs, nest=TRUE)

(nest=TRUE is needed if CPSUM repeats the same values in different 
strata).

Also, if you have access to design variables for the multistage design you 
can use them (but it probably won't make much difference). There's a
very
brief example using the National Health Interview Study at
  http://faculty.washington.edu/tlumley/survey/example-twostage.html


 	-thomas