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Re: st: Linking a patient file with an event file

From   Carl Severson <>
Subject   Re: st: Linking a patient file with an event file
Date   Thu, 28 Feb 2013 10:51:40 -0700

Hi Lisa,

You are on the right track. Try this:

     by id2013: gen edcount = _n
     by id2013: gen temp = _N
     keep if edcount == temp
     drop temp

Now you have one observation per person (making it easy to merge the
visit data to your sociodemographic data) and the variable edcount
will contain a value corresponding to the number of visits each person
had, which I think is what you said you needed.

Good luck.

p.s. I work with the same kind of data all the time so if you have
more questions, feel free to ask.

On Thu, Feb 28, 2013 at 10:15 AM, Health Services PhD
<> wrote:
> I want to link/merge several files, but my data are complicated and
> I’m unsure how to proceed. I'm using Stata 11.2 for Windows.
> My patient file contains sociodemographic information for ~60,000
> patients. My event file contains information about ~20,000 visits to
> emergency rooms. There is a patient ID variable in each file. Many
> patients in my patient file will not be in my event file (because they
> didn't visit the emergency room). My event file has a patient ID,
> service date, and various other variables related to the visit.
> I need to merge the files so I can analyze incidence and run
> regression models. I've read lots about merging files, but haven't
> seen anything that addresses my issue yet.
> I assume I will need to reshape my event file from long to wide so
> that there is one row per patient, but everything I read about
> reshaping assumes that the multiple observations per patient are
> identified somehow. So one thing I *think* I need to do is generate a
> new variable that counts ED visits for each patient. I thought I might
> be able to do something like this: (from
> by id2013: gen edcount = 1 if _n==1
> replace edcount = sum(edcount)
> But that gives me a sequential number that doesn't restart at 1 for
> each new patient ID.
> Is reshaping the right approach, and if so, how do I best create the
> variable I need?
> Thanks in advance for your time,
> Lisa
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