-----Original message-----
On 2008 June 10 moleps islon wrote:
Dear statalisters, can someone help me out with this basic question?
I need to calculate the probability of the following event:
That at least one patient out of 99 suffers from kidneycancer
(incidence 15/100000 pr year) over a time period of 15 years.
Dear Moleps,
searching the literature (Briggs A, Sculpher M, Claxton K. Decision
Modelling for Health Economic Evaluation. Oxford: Oxford University Press,
2006:51) I have found out a formula for converting rate into probabilities:
p=1-exp(-rt)
where:
p=probability;
r= instantaneous rate, provided that it is constant over the period of
interest (t)
Hence, your 15-year probability would be:
Display 1-exp(-15/100000*15)
.00224747
and your 1-year probability would be:
display 1-exp(-15/100000*1)
.00014999 // that is, around 15 new cases per year.
Eventually, I have tried to sketch a temptative answer to your question,
referring to the 1-year probability that at least one patient convert to
kidney cancer:
Display
1/100000+1/99999+1/99998+1/99997+1/99996+1/99995+1/99994+1/99993+1/99992+1/9
9991+1/99990+1/99989+1/99988+1/99987+1/99986
.00015001
I do hope that my last try will not mislead you. Probably, Stata gurus on
the list can support you with a better solution.
HTH and Kind Regards,
Carlo
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