Reply
Mon 1 Dec, 2014 08:55 am
In a town 1/1000 of people suffer from a disease. A medical examination identifies with 99% certainty the condition of the patient, i.e. if he/she is sick, it shows the disease condition in 99% of the cases, if he/she is healthy, it shows the absence of disease in 99% of the cases. (This is equivalent to saying that the sensitivity and specificity of the diagnostic test are both 99%). a. What is probability that the medical examination of a randomly selected person will identify the individual as sick? b. Let us assume that someone has been found sick by the test. What is the probability that he/she is indeed sick?
@iampilgrim,
iampilgrim wrote:
In a town 1/1000 of people suffer from a disease. A medical examination identifies with 99% certainty the condition of the patient, i.e. if he/she is sick, it shows the disease condition in 99% of the cases, if he/she is healthy, it shows the absence of disease in 99% of the cases. (This is equivalent to saying that the sensitivity and specificity of the diagnostic test are both 99%). a. What is probability that the medical examination of a randomly selected person will identify the individual as sick? b. Let us assume that someone has been found sick by the test. What is the probability that he/she is indeed sick?
From 1000 tests, you would expect 999 people to be disease free. One percent of those 9.99 will test positive. The remaining one person is positive and will test positive 0.99. So 0.99 correct positives for every 10.98 positive tests or 9% probability that a test positive is a real positive.
Stumble It!
Tweet This
Bookmark on Delicious
Share on Facebook
Share on MySpace