chapter 3 pg 12
it reads....
Start with BNP of < 50 pg/ml. If the sensitivity of a BNP ≥50 pg/ml is 0.97, then that must mean 3% of those with CHF were falsely negative, and P(BNP<50|CHF)=3%.
i don't understand how this part is true: P(BNP<50|CHF)=3%
can anyone explain?
Hi, Laura --
If you have CHF, then a test for it can either be a true positive or a false negative. (That is, if you have the disease you know you are in the left column of the 2 x 2 table.)
So if sensitivity = P(BNP >= 50 pg/ml) =0.97 then 1- sensitivity = P (BNP < 50 pg/ml) must be 0.03, because >=50 and <50 are the only 2 possibilities.
Does that help?
Tom
P(BNP<50|CHF) means "the probability of a BNP less than 50 pg/ml given congestive heart failure"
People with CHF tend to have very high BNP levels. Only 3% of them will have a BNP < 50,
