Relative Risk Calculator — 公式
## How to Calculate Relative Risk
### Formula
**RR = [a / (a+b)] / [c / (c+d)]**
Relative risk compares the probability of an event in the exposed group to the probability in the unexposed group. RR = 1 means no difference. RR > 1 means higher risk in the exposed group. RR < 1 means the exposure is protective. The Number Needed to Treat (NNT) = 1 / |Risk Difference|.
### Formula
**RR = [a / (a+b)] / [c / (c+d)]**
Relative risk compares the probability of an event in the exposed group to the probability in the unexposed group. RR = 1 means no difference. RR > 1 means higher risk in the exposed group. RR < 1 means the exposure is protective. The Number Needed to Treat (NNT) = 1 / |Risk Difference|.
计算示例
Group 1: 30 events out of 100. Group 2: 15 events out of 100.
- Risk Group 1 = 30 / (30+70) = 30/100 = 0.30
- Risk Group 2 = 15 / (15+85) = 15/100 = 0.15
- RR = 0.30 / 0.15 = 2.0
- Risk Difference = 0.30 - 0.15 = 0.15
- NNT = 1 / 0.15 ≈ 6.67
- Group 1 has twice the risk; for every ~7 people treated, one event is attributable to exposure.