st: power calculation and sample size

["stata_user stata_user" <stata_dofile@hotmail.co.uk>]

Dear All,

I would be highly thankful to you if you let me know the way in which sample 
size can be calculated for the following problem

I am studying the occurrence of a  disease between two groups.
I have an annual average event rate of 1.6 % and a follow up period of 5 
years, I want to have a power of 80%  with alpha  5% I am looking to detect  
a relative risk of 3.0 associated with  group1 versus group 2 .

I am trying to find the best way to do this in stata,


Thank you very much ,

Regards,

Sami

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