reciprocal of difference number needed to screen to detect NNS A statistic that represents the number of units that needs to be tested to identify one additional case. The Number Needed to Screen to Detect is calculated as the reciprocal of a difference in rate of detected cases with and without screening. The Number Needed to Screen (NNS) value is often rounded up to the next highest whole integer. The Number Needed to Screen to Detect is distinct from the Number Needed to Screen to Prevent as the formulas to calculate are different, even though both may be abbreviated as NNS. Expert Working Group Agreement: 2022-08-03 vote 5-0 by Jesus Lopez-Alcalde, Janice Tufte, Eric Harvey, Philippe Rocca-Serra, Harold Lehmann Brian S. Alper, Harold Lehmann, Joanne Dehnbostel, Kenneth Wilkins, Janice Tufte ready for release