Re:Half of women will get a false positive 3D mammogram, stu...
by csee on Saturday March 26, 2022 @11:08PM
(#30817401)
I believe this is wrong.
Positive predictive value is the likelihood that, if you have gotten a positive test result, you actually have the disease. It’s calculated as TP/TP+FP.
TP, ie true positives, is a function of false negatives.
Here's a common sense explanation. Assume the false negative rate is 100% and so you have zero true positives. Then every positive test result will be a false positive, and therefore a positive test result shows that you don't have the disease.
On the other hand, assume the false negative rate is 0. Then a positive test result will mean that you probably do have the disease as long as the false positive rate isn't too high.
Remember your post I was replying to was all about the probability that you actually have the disease conditional on a positive test result. That's the question I am addressing. For this question, you must consider the false negative rate.
Positive predictive value is the likelihood that, if you have gotten a positive test result, you actually have the disease. It’s calculated as TP/TP+FP.
TP, ie true positives, is a function of false negatives.
Here's a common sense explanation. Assume the false negative rate is 100% and so you have zero true positives. Then every positive test result will be a false positive, and therefore a positive test result shows that you don't have the disease.
On the other hand, assume the false negative rate is 0. Then a positive test result will mean that you probably do have the disease as long as the false positive rate isn't too high.
Remember your post I was replying to was all about the probability that you actually have the disease conditional on a positive test result. That's the question I am addressing. For this question, you must consider the false negative rate.