--- Ziad El-Khatib <[email protected]> wrote:
> we observed patients at different time points and it is numbered
> under 'visit' variable as 1,2,3,4,5
>
> And we know the date of each visit (variable named 'date')
>
> I am trying to calculate the number of days between visits for each
> patient. Patients can be identified after their studyid.
>
> For example, my aim is to have something as below
>
> studyid visit date days
> 1001 1 01-01-2000 0
> 1001 2 15-01-2000 14
> 1001 3 20-01-2000 5
>
> etc..
turn the date variable into a Stata date variable and than you can
within each studyid subtract the current date from the previous date,
see -help date-, -help by- and the example below:
*-------------------- begin example -------------------
clear
input long studyid visit str10 date
1001 1 01-01-2000
1001 2 15-01-2000
1001 3 20-01-2000
end
gen ndate = date(date, "DMY")
format ndate %td
bys studyid (ndate) : gen days = cond(_n == 1, ///
0, ///
ndate - ndate[_n-1])
*-------------------- end example ----------------------
(For more on how to use examples I sent to the Statalist, see
http://home.fsw.vu.nl/m.buis/stata/exampleFAQ.html )
Hope this helps,
Maarten
-----------------------------------------
Maarten L. Buis
Department of Social Research Methodology
Vrije Universiteit Amsterdam
Boelelaan 1081
1081 HV Amsterdam
The Netherlands
visiting address:
Buitenveldertselaan 3 (Metropolitan), room Z434
+31 20 5986715
http://home.fsw.vu.nl/m.buis/
-----------------------------------------
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