00:01
The probability of having a particular disease is 0 .04.
00:04
So we're going to have probability of having this disease, d, 0 .04.
00:11
Okay, and we have a lot of information on it.
00:14
I'm just going to try and turn it all into probability notation to make it clearer.
00:18
So we have a test.
00:20
If the disease is present, the probability of a positive result is 0 .92.
00:25
So probability of a positive result, given that they have the disease is 0 .92.
00:31
If they don't have the disease, the probability of a positive result is 0 .02.
00:38
So probability positive given no disease is not.
00:43
Okay, so a positive result is received.
00:48
What's the probability they actually have the disease? so we want the probability of having the disease given a positive result.
00:58
Great, so we've turned this paragraph into our probability notation, and when you want to switch around the conditional probability like this, you use bay's rule.
01:09
There's a formula to help us.
01:13
So we're using bay's rule, and the formula is that the probability of b given a is equal to the probability of a multiplied by the probability of b divided by the probability of a.
01:32
So let's apply that to this particular case.
01:34
Make some space for it.
01:43
So we need the probability of positive given disease, which we have.
01:49
We need the probability of having the disease, which we have...