Number needed to screen

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The number needed to screen is a way of summarizing the benefit of a screening program in health care.[1] The calculations are derived from the results of a randomized controlled trial of a screening program.

Two-by-two table for a screening program
Outcome
Present Absent
Screening Screen group Cell A Cell BTotal in screening group
Control group Cell C Cell DTotal in control group
Total with outcome Total without outcome

Contents

Calculations

Event rates

\mbox{Experimental event rate}=\left (\frac{\mbox{Cell A}}{\mbox{Cell A + Cell B}}\right )
\mbox{Control event rate}=\left (\frac{\mbox{Cell C}}{\mbox{Cell C + Cell D}}\right )

Measures of efficacy

\mbox{Absolute risk reduction} =\left (\mbox{Experimental event rate} - \mbox{Control event rate}\right )
\mbox{Number need to screen}=\left (\frac{100}{\mbox{Absolute risk reduction}}\right )

Example

References

  1. ↑ Rembold CM (1998). Number needed to screen: development of a statistic for disease screening. BMJ 317 (7154): 307–12. PMID 9685274.

See also

Mass screening

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