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The sensitivity of an electronic device, e.g., a communications system receiver, or detection device, e.g., PIN diode, is the minimum input signal required to produce a specified output signal having a specified signal-to-noise ratio, or other specified criteria.

Note 1: The signal input may be expressed as power in dBm or as field strength in microvolts per meter, with input network impedance stipulated.

Note 2: "Sensitivity" is sometimes improperly used as a synonym for "responsivity."

Source: from Federal Standard 1037C and from MIL-STD-188

The sensitivity of a binary classification test or algorithm, such as a blood test to determine if a person has a certain disease, or an automated system to detect faulty products in a factory, is a parameter that expresses something about the test's performance. The sensitivity of such a test is the proportion of those cases having a positive test result of all positive cases (eg, people with the disease, faulty products) tested. A sensitivity of 100% means that all sick people or faulty products were recognized as such, but it alone doesn't tell us all about the test, as a 100% sensitivity can be trivially achieved by labeling all test cases positive, despite of their true status. For more information see binary classification. See also specificity.

In the traditional language of statistical hypothesis testing, the sensitivity of a test is called the power of the test, although the word power in that context has a more general usage that is not applicable in the present context.

In the context of information retrieval, the concept of sensitivity is also known as recall.

The sensitivity of a human, often considered with regard to a particular kind of stimulus, is the strength of the feeling it results in, in comparison with the strength of the stimulus. The concept applies to physical as well as emotional feeling.