calling dr killdare

If the test is 99% accurate, and yours came back positive, then there is a 99% chance that you have the disease.

If the test is to show you are sick, (positive = sick), it's a 99% chance you are sick.
If the test is to show you are healthy, (positive = healthy), it's a 50-50 chance you're sick.
(If the test is inconclusive, there's a 98% - 99% chance you are sick.)

Note: I have obviously assumed parameters that may not be the case, e.g. all but 99% are healthy, or sick; and that 1% is inaccurate and just not inconclusive, if even only in part.

11/122

Is that about 9% Mark? How did you arrive at that? It's so differrent from whar some of the others say.

my feeling was that it be 50%

When you say "the test is 99% accurate", do you mean that for every 100 people with the disease who are tested, there are 99 positive results? Or do you mean that for every 100 people without the disease, there is one positive result? Or what?

Yes, about 9%. Assume a population of 100,000. 100 are sick.

So, if you test positive, the probability is 99/(99+999) that you are sick.