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In COVID-19 testing, what does number needed to test mean?

"Number needed to test" is the number of individuals in the target population who would need to be tested under a given strategy to find, in expectation, one case of SARS-CoV-2. The number needed to test is the inverse of the efficiency. For example, if 100 people were tested and 6 were identified as cases, the number needed to test to identify one SARS-CoV-2-positive case in that strategy would be 100/6 = 16.67. In this example, 17 individuals would need to be tested to identify one case.

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