Calculate attributable risk (risk difference), the attributable fraction among the exposed and the number needed to harm from counts or risks.
About this tool
Risk difference and attributable fraction among the exposed.
How to use Attributable Risk Calculator
- Enter cases and totals for exposed and unexposed groups, or the two risks.
- Choose the confidence level.
- Read the attributable risk, attributable fraction and NNH.
Worked example
A risk of 6% in smokers and 2% in non-smokers gives an attributable risk of 4% (40 extra cases per 1,000) and an attributable fraction of 66.7%.
What does the attributable fraction mean?
The share of cases among the exposed that would not occur without the exposure, assuming the link is causal.
How is it different from population attributable risk?
Attributable risk concerns the exposed group only; population attributable risk also accounts for how common the exposure is.
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