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False positive


A test result in which the test is positive (for example, a positive pregnancy test) but the event is not extant (the woman is not pregnant): also called a 'false alarm'. The trouble with false positives is that the more you test the more apparent disease you find, also called a false-positive explosion.

False positive rate

The proportion of positive tests among people without the disease or condition. It is typically expressed as a conditional probability or a percentage. For instance, if mammography screening has a false positive rate of 5 to 10% depending on age, that is 5 to 10% of women without breast cancer nevertheless receive a positive test result. The false positive rate and the specificity (power) of a test add up to 100%. The false positive rate and the false negative rate are dependent: to decrease one is to increase the other.