In: Statistics and Probability
In a population, 28 % of people have a disease called D, a certain kind of skin problem, among them 42 % will develop into skin cancer. For people without this skin problem (D), only 8 % will have skin cancer.
a) What is the rate of skin cancer in this population
b) If a person found out that he has skin cancer, what is the chance that he had skin problem (D)?
Let A defines an event of getting a skin disease.
Ac defines an event of not getting skin disease.
It is given that 28% of people have D-disease. Hence, P(A) = 0.28 and P(Ac) = 0.72
Let B defines an event of developing skin cancer.
Among those diseased people 42% people will develop into skin cancer. Hence, probability that people will develop skin cancer given that they have skin disease D is 0.42. Hence, P( B|A ) = 0.42
For people without skin problem, only 8% will have skin cancer. Hence, probability of having skin cancer given that the person is not having skin disease is 0.08. That is, P( B|Ac ) = 0.08
(a) - We need to find the rate of skin cancer. That is P( B )
The Law of total probability states that,
Hence, the rate of skin cancer in the population is 17.52%
(b) -
We need to find the chance that the person had a skin problem given that he has a skin cancer. That is P( A|B )
According to the Baye's theorem,
Hence, If a person found out that he has a skin cancer, there is 67.12% chance that he had skin problem.
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