Sensitivity and specificity are statistical
measures of the performance of a
binary classification test, also known in
statistics as classification function.
Sensitivity (also called the true positive rate, or
the recall rate in some fields) measures the
proportion of actual positives which are correctly
identified as such (e.g. the percentage of sick
people who are correctly identified as having the
Imagine a study evaluating a new test that screens people for a disease. Each person taking the
test either has or does not have the disease. The test outcome can be positive (predicting that
the person has the disease) or negative (predicting that the person does not have the disease).
The test results for each subject may or may not match the subject's actual status. In that setting:
True positive: Sick people correctly diagnosed as sick
False positive: Healthy people incorrectly identified as sick
True negative: Healthy people correctly identified as healthy
False negative: Sick people incorrectly identified as healthy
Sensitivity relates to the test's ability to identify a condition correctly. Consider the
example of a medical test used to identify a disease. Sensitivity of the test is the
proportion of people known to have the disease, who test positive for it.
Precision and recall
In pattern recognition and information retrieval
with binary classification, precision (also called
positive predictive value) is the fraction of
retrieved instances that are relevant, while recall
(also known as sensitivity) is the fraction of
relevant instances that are retrieved
there is an inverse relationship
between precision and
recall, where it is possible to
increase one at the cost of
reducing the other.