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Re: st: using several years of survey data
From
Rebecca Pope <[email protected]>
To
[email protected]
Subject
Re: st: using several years of survey data
Date
Wed, 2 Mar 2011 14:11:29 -0600
Maria,
If you haven't already, you should consult the following documents
from HCUP (for those not familiar, HCUP publishes the NIS):
- Calculating Nationwide Inpatient Sample Variances
http://www.hcup-us.ahrq.gov/reports/methods/CalculatingNISVariances200106092005.pdf
- Using the HCUP Nationwide Inpatient Sample to Estimate Trends
http://www.hcup-us.ahrq.gov/reports/methods/2006_05_NISTrendsReport_1988-2004.pdf
Combined, I think they'll answer any set-up questions you have. I
especially recommend the Trends document because the sampling frame
for the NIS has changed over time, as have their sample selection
methods (including strata definitions). They have guides for coping
with this in your research. There is also sample Stata code (in the
Variances document), though depending on which version of Stata you
are using, you will probably need to change the syntax. They use
version 8.
If you have already read these documents & weren't able to have your
questions sufficiently answered, I endorse Steve's recommendation to
contact HCUP. The HCUP Technical Assistance contact information is all
online & in my experience they are very responsive.
Regards,
Rebecca
On Wed, Mar 2, 2011 at 1:02 PM, Steven Samuels <[email protected]> wrote:
>
> Maria, ordinarily I would say that your set up is correct. However, sometimes in this kind of study (I'm not familiar with yours), the population is randomly divided into five groups of about equal size; then one group a year is surveyed. In 10 years, each group would appear twice. In this case, I don't know if the standard sampling formulas apply. I suggest that you contact the study statisticians for some guidance.
>
> Steve
> [email protected]
>
>
> On Mar 1, 2011, at 4:22 PM, Maria E. Montez Rath wrote:
>
> 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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