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Re: st: Difference in values within the same variable
From
Sara Muller <[email protected]>
To
[email protected]
Subject
Re: st: Difference in values within the same variable
Date
Tue, 03 Jan 2012 14:20:23 +0000
Thank you - that works perfectly.
Sara
Dr Sara Muller
National School for Primary Care Research Fellow
Arthritis UK Primary Care Centre
Primary Care Sciences
Keele University
Keele
Staffordshire
ST5 5BG
Tel 01782 734842
Fax 01782 733911
www.keele.ac.uk/pchs
On 03/01/2012 14:06, Christopher Baum wrote:
<>
Sara said
I have long data with multiple prescriptions per person. I want to
define the length of time between successive prescriptions (see data
below, which is sorted by patid (person ID) and presc_date (date of
prescription)), with the eventual aim of including in my analysis only
people who received 2 or more prescription within 6 months of each other.
I'm not bothered really how I do this, although I have been trying to do
it by calculating another variable that gives the time from the previous
prescription (within patid). I believe the equivalent command in SPSS is
called a 'lag', but searching for this in Stata doesn't see to have
turned up the right stuff.
--------------
clear all
input patid str9 presc_date
4457 11aug1997
4457 18aug1997
4457 15sep1997
4457 29sep1997
4457 27oct1997
4457 15dec1997
4457 15dec1997
4457 16apr1998
4457 11may1998
end
g rxd = date(presc_date,"DMY")
format rxd %td
bysort patid (rxd): g timesince = rxd[_n] - rxd[_n - 1]
list
-----------------
Kit Baum | Boston College Economics& DIW Berlin | http://ideas.repec.org/e/pba1.html
An Introduction to Stata Programming | http://www.stata-press.com/books/isp.html
An Introduction to Modern Econometrics Using Stata | http://www.stata-press.com/books/imeus.html
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