Ziad wrote:
I want to calculate the number of days elapsed between date of
patients visits to the clinic, patients are expected to come each 4th
week, i.e. week4, week8, week12 etc..
I have date of visit (var date) and dummy variable for weeks, i.e.
week4 (1 or 0), week8 (1 or 0)
I am trying to generate new variable to calculate n of days between
week8 and week4, by saying dayat8 = (date if week4==1) - (date if
week8==1) it does not work
----------------------------------------------------
This is not legal syntax:
generate dayat8 = (date if week4==1) - (date if week8==1)
I guess that your data are in long format, with one observation
for each patient and visit, i.e. that the dates for the week4 and
week8 visits are in different observations:
+--------------------------------------------+
| patid date week4 week8 week12 |
|--------------------------------------------|
1. | 1 10jan2007 1 0 0 |
2. | 1 07feb2007 0 1 0 |
3. | 1 07mar2007 0 0 1 |
+--------------------------------------------+
They must be brought together:
clear
input patid str9 sdate week4 week8 week12
1 10jan2007 1 0 0
1 07feb2007 0 1 0
1 07mar2007 0 0 1
end
// generate date = date(sdate,"dmy") // Stata 9 syntax
generate date = date(sdate,"DMY") // Stata 10 syntax
// format date %d // Stata 9 syntax
format date %td // Stata 10 syntax
generate week=4 if week4==1
replace week=8 if week8==1
replace week=12 if week12==1
drop week4 week8 week12 sdate
reshape wide date , i(patid) j(week)
generate dayat8 = date8-date4
list
+----------------------------------------------------+
| patid date4 date8 date12 dayat8 |
|----------------------------------------------------|
1. | 1 10jan2007 07feb2007 07mar2007 28 |
+----------------------------------------------------+
Hope this helps
Svend
__________________________________________
Svend Juul
Institut for Folkesundhed, Afdeling for Epidemiologi
(Institute of Public Health, Department of Epidemiology)
Vennelyst Boulevard 6
DK-8000 Aarhus C, Denmark
Phone: +45 8942 6090
Home: +45 8693 7796
Email: [email protected]
__________________________________________
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