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st: Comparing continuation rates for drugs with different durations of use


From   Paul O Brien <paul.obrien@afe2.org.uk>
To   statalist@hsphsun2.harvard.edu
Subject   st: Comparing continuation rates for drugs with different durations of use
Date   Tue, 1 Nov 2005 08:10:27 +0000

Database of visits to clinic for two contraceptivesa new implant which last for 3 years and the contraceptive injection which needs to be topped-up every 12 weeks.

I want to compare the continuation rates for new users starting year 2000.

The start date for the implant is the date of insertion and terminal date the day of removal.

The difficulty is with the second method, the injection. The start date it the date of first injection (i.e. has not had an injection in the previous 16 weeks), and the terminal date is 12 weeks after the last injection, if she has not had another within 16 weeks. A patient who returns for injection 15 week after the last one is considered to be still using the method, but has discontinued if she return 16 weeks after the previous one. How do I identify the start and end dates?

Those still using will be censored.

Thanks.

Paul

-------------------------------
Paul O Brien
Raymede Clinic
Exmoor St
London
W10 6DZ
44 + (0)20 + 8962 4450




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