Re:Medicine’s Uncomfortable Relationship with Math (2014)
by timbre on Sunday March 20, 2016 @09:10PM
(#11325569)
That's what a "false positive" is but Wikipedia also has a separate article on "false positive rate", which gives the formula
FP / (FP + TN)
Where FP is number of false positives, and TN is number of true negatives. So it's a third option:
- Out of 1000 actually negative samples, 50 were tested as positive.
So in the case of 1000 samples, 949 correctly testing as negative, 50 incorrectly testing as positive, and 1 correctly testing as positive, the false positive rate is 50 / 999.
FP / (FP + TN)
Where FP is number of false positives, and TN is number of true negatives. So it's a third option:
- Out of 1000 actually negative samples, 50 were tested as positive.
So in the case of 1000 samples, 949 correctly testing as negative, 50 incorrectly testing as positive, and 1 correctly testing as positive, the false positive rate is 50 / 999.