Relative risk reduction
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The relative risk reduction is a measure used in epidemiology. It is calculated by dividing the absolute risk reduction by the control event rate.[1][2][3][4]
The relative risk reduction can be more useful than the absolute risk reduction in determining an appropriate treatment plan, because it accounts not only for the effectiveness of a proposed treatment, but also for the relative likelihood of an incident (positive or negative) occurring in the absence of treatment.
Like many other epidemiological measures, the same equations can be used to measure a benefit or a harm (although the signs may need to be adjusted, depending upon how the data was collected.)
Worked example
| Abbreviation | Variable | Equation | Value |
| - | subjects in control group | - | 250 |
| - | subjects in experimental group | - | 150 |
| - | events in control group | - | 100 |
| - | events in experimental group | - | 15 |
| CER | control event rate | = events / subjects in control group | 0.4, or 40% |
| EER | experimental event rate | = events / subjects in experimental group | 0.1, or 10% |
| ARR | absolute risk reduction (or increase) | = CER - EER | 0.3, or 30% |
| RRR | relative risk reduction (or increase) | = (CER - EER) / CER | 0.75 |
| NNT | number needed to treat/number needed to harm | = 1 / ARR | 3.33 |
| OR, RR | odds ratio, relative risk (not really identical, but similar -- see articles for details) | = CER / EER | 4 |
References
- ↑ Barratt A, Wyer P, Hatala R, McGinn T, Dans A, Keitz S, Moyer V, For G (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. PMID 15313996.
- ↑ http://evidence.ahc.umn.edu/arr-s5.htm
- ↑ http://www.jr2.ox.ac.uk/bandolier/booth/glossary/Rrisk.html
- ↑ http://gim.unmc.edu/dxtests/Effect1.htm
Acknowledgement and Attribution Regarding Sources of Content
Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .
