Relative Risk Calculator

The relative risk calculator can be used to estimate the relative risk (or risk ratio) and its confidence interval for two different exposure groups.

Enter the data into the table below, select the required confidence level from the dropdown menu, click "Calculate" and the results will be displayed below.

Relative Risk (Risk Ratio) Calculator
Disease No Disease Total
Exposed Group A = B = ? = A + B
Not Exposed Group C = D = ? = C + D

The relative risk calculator uses the following formulas:

Relative Risk (RR) = [A/(A+B)] / [C/(C+D)] = Probability of Disease in Exposed / Probability of Disease in Unexposed

Interpretation:

  • If Relative Risk = 1, there is no association
  • If Relative Risk < 1, the association is negative
  • If Relative Risk > 1, the association is positive

Lower Bound of Confidence Interval (LB) = exp( ln(RR) − z * (1/A + 1/C − 1/(A + B) − 1/(C + D)) 1/2 )

Upper Bound of Confidence Interval (UB) = exp( ln(RR) + z * (1/A + 1/C − 1/(A + B) − 1/(C + D)) 1/2 )

Where z is the z-score corresponding to the desired confidence level (e.g., for a 95% confidence level, z = 1.96)

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