In: Statistics and Probability
Assume breast cancer affects 0.005 of the female population between 45 and 55 years of age. There are two kinds of positive test results: -True positive (the test indicates you have a disease, and you actually have it) -False positive (the test indicates you have a disease, but you actually do not) Assume mammograms are: 0.932 accurate detecting people who actually have breast cancer (true positive rate) 0.91 accurate for people who do not have breast cancer (true negative rate) Compute the probability that a female between the ages of 45 and 55 who tests positive for breast cancer has breast cancer, and enter your answer with 3 decimal places.
P(have breast cancer) = 0.005
P(positive test | have breast cancer) = 0.932
P(negative test | don't have breast cancer) = 0.91
P(positive test | don't have breast cancer) = 1 - P(negative test | don't have breast cancer) = 1 - 0.91 = 0.09
P(positive test) = P(positive test | have breast cancer) * P(have breast cancer) + P(positive test | don't have breast cancer) * P(don't have breast cancer)
= 0.932 * 0.005 + 0.09 * (1 - 0.005)
= 0.0942
P(has cancer | positive test) = P(positive test | have breast cancer) * P(have breast cancer) / P(positive test)
= 0.932 * 0.005 / 0.0942
= 0.049 (ans)