st: using several years of survey data

["Maria E. Montez Rath" <maria.rath@gmail.com>]

Hello,

I'm using 10 years of the National Inpatient Sample (NIS) and have a
question on how to define the strata.

The NIS is a stratified, single-stage cluster sample of hospitals.
Every year, about 20% of US community hospitals are sampled. Sixty
strata are defined depending on things like geographical region and
teaching status, and from each a random sample of hospitals is taken.
For each hospital all discharges are then selected.

The data provided includes the strata and weights. I set the data by

svyset hospid [pweight=discwt], strata (nis_stratum)

When using several years, shouldn't I create a new strata variable
that incorporates the year so that the strata is different per year?

gen str yearstratum=string(year,"%04.0f") + string( nis_stratum,"%04.0f")

svyset hospid [pweight=discwt], strata (yearstratum)

I think this is necessary in order to obtain the correct standard errors.

Can anyone correct me if I'm wrong or confirm that what I'm doing is right?

Thank you,

Maria

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