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Re: st: probability question


From   Richard Williams <Richard.A.Williams.5@ND.edu>
To   statalist@hsphsun2.harvard.edu, statalist@hsphsun2.harvard.edu
Subject   Re: st: probability question
Date   Tue, 10 Jun 2008 18:35:50 -0500

At 03:17 PM 6/10/2008, 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.
Sounds like a good exam question. I think it is easier to figure out the probability that no one gets kidney cancer. The probability of one person not getting kidney cancer in a year is 1 - 15/100000. The probability of one person not getting kidney cancer over 15 years is (1 - 15/100000)^15. The probability that 99 people will be so lucky is (1 - 15/100000 )^15^99:

. di (1 - 15/100000 )^15^99
.80030153

So, the probability that at least 1 gets kidney cancer is

. di 1 - ((1 - 15/100000 )^15^99)
.19969847

So, there is about a 20% chance at least one person gets kidney cancer.

Someone can feel to correct me if I am wrong!



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Richard Williams, Notre Dame Dept of Sociology
OFFICE: (574)631-6668, (574)631-6463
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EMAIL: Richard.A.Williams.5@ND.Edu
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