00:01
Suppose that one person in 100 ,000 has a particular rare disease for which there is, i'm sorry, a fairly accurate diagnostic test.
00:10
This test is correct 99 % of the time.
00:14
So let's go ahead and do, i'm going to make a little bit of a chart here.
00:19
So this would be that we have and that we do not have.
00:24
So one in 100 ,000 would be 0 .000 -0 -0 -01.
00:31
Which means this would be 0 .9999.
00:36
And then we could test positive or we could test negative.
00:43
And then here we could do the same thing.
00:45
We could test positive or we could test negative.
00:49
Now, testing positive when you have it, it's 99%.
00:54
So 0 .99, which means negative would be 0 .01.
00:59
And then testing, the test is correct 99 .5 % of the time when given to a person's less, at random who does not have the disease.
01:06
So being negative and testing negative, so that's the correct test would be .995 .005.
01:13
So with that in play, let's go ahead and answer our probabilities.
01:17
So the first part is the probability of testing positive for the disease who has the disease.
01:28
So we're going to do the probability of testing positive and having the disease.
01:33
So that's 0 .2, 2, 3, 4, 1 .0 .01 times .99...