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Population Attributable Risk Calculator

Work out population attributable risk instantly with clear inputs, formula shown and shareable results.

About Population Attributable Risk Calculator

Applies Levin's formula to convert exposure prevalence and relative risk into the share of cases attributable to the exposure.

Formula

Levin's formula

PAF = p(RR - 1) / (1 + p(RR - 1)), where p is exposure prevalence; attributable cases = PAF x total cases

Worked example

With the default values below, Population Attributable Risk Calculator returns Population attributable fraction of 31.034%. Change any input above and every figure here is recalculated in your browser.

Inputs used

Exposure prevalenceaccepts 0.1–100
30
Relative riskaccepts 0.1–30
2.5
Total cases in the populationaccepts 1–10,000,000
4,000

Results

Population attributable fraction
31.034%
Cases attributable to the exposure
1,241.4
Cases remaining if exposure were removed
2,758.6
Excess risk contribution term
0.4500

Step by step

  1. 1Values used
  2. 2Levin's formula
  3. 3Population attributable fraction= 31.034
  4. 4Cases attributable to the exposure= 1,241.4
  5. 5Cases remaining if exposure were removed= 2,758.6
  6. 6Excess risk contribution term= 0.4500

Assumptions and limits

  • The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why can attributable fractions sum above 100%?

Multiple causes can each be necessary for the same case, so fractions for different risk factors overlap.

Does PAF imply causation?

Only if the relative risk is causal; applying it to a confounded association overstates preventable burden.

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