False Positive
Etymology
“Positive” is from Latin “positivus” (formally laid down), from ponere (to place); in testing, a “positive” result asserts the condition is present. The pairing with “false” comes from signal-detection and diagnostic medicine.
noun phrase · /FAWLS POZ-ih-tiv/
A test result that wrongly signals a condition is present when it is not.
What it names
It shows why even an accurate test can produce mostly wrong alarms when the thing it looks for is rare.
Example
If a disease affects 1 in 10,000 people, a 99 percent accurate test flags so many healthy people that most positives are false positives.
Related idea
A false positive is the opposite error to a false negative, and which one a test is tuned to avoid is a value judgment — a smoke alarm accepts false positives to prevent a deadly false negative.