Bayes Theorehl 1- Finding predictive values 2- Determine false positive and fals

Question

Bayes Theorehl 1- Finding predictive values 2- Determine false positive and false negative, sensitivity and specificity 3- Problem sets 1- A scientist designed a medical test for a certain disease. Among 100 patients who have the disease, the test will show the presence of the disease in 96 cases out of 100, and will fail to show the presence of the disease in the remaining 4 cases out of 100. Among those who do not have the disease, the test will erroneously show the presence of the disease in 3 cases out of 100, and will show there is no disease in the remaining 97 cases out of 100 What is the probability that a patient who tested positive on this test actually has the disease, if it is estimated that 20% of the population has the disease? a) B) What is the probability that a patient who tested negative on this test actually does not have the disease, if it is estimated that 4% of the population has the disease?

Explanation / Answer

a)probability of tested postiive =P(have disease and tested positive+not have disease and tested positive)

=0.20*(96/100)+0.8*(3/100)=0.216

therfore probability of having disease given tested positive =P(have disease and tested positive)/P(tested positive)

=0.20*(96/100)/0.216=0.8889

b)

probability of tested negative =P(have disease and tested negative+not have disease and tested negative)

=0.04*(4/100)+0.96*(97/100)=0.9328

therefore probability=P(not have disease|tested negative)=0.96*(97/100)/0.9328=0.9983

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