Absolute risk reduction

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In clinical epidemiology and evidence-based medicine, the absolute risk reduction is a measure that compares the frequency of a clinical outcome in group of patients exposed to a factor compared to a control group of patients.[1] This measure should be contrasted with the relative risk reduction.

Most scientific journal articles fail to report absolute measures which may lead to exaggerated perceptions of results.[2]

Calculations

Two-by-two table for a randomized-controlled trial or cohort study
Outcome
Present Absent
Experimental group Cell A Cell BTotal in the experimental group
Control group Cell C Cell DTotal in the control group
Total with the outcome Total without the outcome
\mbox{Experimental event rate EER)} =\left (\frac{\mbox{ Cell A}}{\mbox{Total in the }experimental\mbox{ group}}\right )
\mbox{Control event rate (CER)} =\left (\frac{\mbox{Cell C}}{\mbox{Total in the }control\mbox{ group}}\right)
\mbox{Absolute risk reduction} =\left (\mbox{CER - EER}\right)

References

  1. ↑ Barratt A, Wyer PC, Hatala R, et al (2004). Tips for learners of evidence-based medicine: 1. Relative risk reduction, absolute risk reduction and number needed to treat. CMAJ 171 (4): 353–8. DOI:10.1503/cmaj.1021197. PMID 15313996.
  2. ↑ Welch HG et al.Ratio measures in leading medical journals: structured review of accessibility of underlying absolute risks.BMJ. 2006 Dec 16;333(7581):1248. Epub 2006 Oct 23. PMID 17060338

See also

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