Question

Suppose that a medical test has a 92% chance of detecting a disease if the person has it (i.e., 92% sensi- tivity) and a 94% chance of correctly indicating that the disease is absent if the person really does not have the disease (i.e., 94% specificity). Suppose 10% of the popu- lation has the disease. (a) What is the probability that a randomly chosen per- son will test positive

Answer 1

14.6% probability that a randomly chosen person will test positive

Explanation:

We have these following probabilities:

10% probability that a randomly selected person has the disease.

If a person has the disease, 92% probability of testing positive.

100-10 = 90% probability that a person does not have the disease.

If a person does not have the disease, 100-94 = 6% probability of testing positive.

What is the probability that a randomly chosen person will test positive

92% of 10% or 6% of 90%.

Then

p = 0.92*0.1 + 0.06*0.9 = 0.146

14.6% probability that a randomly chosen person will test positive