Relative Risk Reduction (RRR)

The proportional reduction in the rate of an adverse outcome in the treatment group compared to the control group, calculated as (control event rate minus treatment event rate) divided by the control event rate. RRR can overstate clinical benefit when baseline risk is low, making absolute risk reduction (ARR) and number needed to treat (NNT) important complementary measures for clinical decision-making.

例

• Statin therapy: 25% RRR in cardiovascular events (but ARR only 2-3% in primary prevention)
• Tamoxifen: 49% RRR in breast cancer recurrence in ER-positive disease
• COVID-19 mRNA vaccine: 95% RRR in symptomatic infection in pivotal trials