U01.06.008 Relative risk reduction

Relative Risk Reduction (RRR) is the proportion of risk reduction attributable to an intervention compared to a control. It measures how much the risk is reduced in the treatment group relative to the control group.

Calculation of Relative Risk Reduction

RRR can be calculated using the following formula:

RRR=1−Relative Risk (RR)\text{RRR} = 1 – \text{Relative Risk (RR)}RRR=1−Relative Risk (RR)

Where: RR=Incidence in Treatment GroupIncidence in Control Group\text{RR} = \frac{\text{Incidence in Treatment Group}}{\text{Incidence in Control Group}}RR=Incidence in Control GroupIncidence in Treatment Group

Example Calculation

Consider a scenario where 2% of patients who receive a flu shot develop the flu, while 8% of unvaccinated patients develop the flu. The relative risk (RR) and relative risk reduction (RRR) can be calculated as follows:

Relative Risk (RR): RR=2%8%=28=0.25\text{RR} = \frac{2\%}{8\%} = \frac{2}{8} = 0.25RR=8%2%=82=0.25
Relative Risk Reduction (RRR): RRR=1−0.25=0.75\text{RRR} = 1 – 0.25 = 0.75RRR=1−0.25=0.75This means there is a 75% reduction in the risk of developing the flu for vaccinated patients compared to unvaccinated patients.

Table: Relative Risk and Relative Risk Reduction Example

Group	Incidence of Flu	Relative Risk (RR)	Relative Risk Reduction (RRR)
Vaccinated (Treatment)	2%	0.25	75%
Unvaccinated (Control)	8%	–	–

Table: Relative Risk and Relative Risk Reduction Example

Points to Remember

RRR provides a measure of how much an intervention decreases the risk of an outcome relative to the control group.
RR is the ratio of the incidence of an outcome in the treatment group compared to the control group.
RRR is often used in clinical trials to compare the effectiveness of different treatments.

Bibliography

Guyatt, G., Rennie, D., Meade, M. O., & Cook, D. J. (2014). Users’ Guides to the Medical Literature: A Manual for Evidence-Based Clinical Practice (3rd ed.). McGraw-Hill Education.
Altman, D. G., & Bland, J. M. (1994). Statistics Notes: The Relative Risk Reduction, Absolute Risk Reduction, and Number Needed to Treat. BMJ, 309(6947), 1461-1462.
Rothman, K. J., Greenland, S., & Lash, T. L. (2008). Modern Epidemiology (3rd ed.). Lippincott Williams & Wilkins.

USMLE Step 1 Review Series

Curriculum

U01.06.008 Relative risk reduction

Calculation of Relative Risk Reduction

Example Calculation

Table: Relative Risk and Relative Risk Reduction Example

Points to Remember

Bibliography

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