Risk Calculator: Relative Risk, ARR, NNT and Odds Ratio

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Use "counts" if you have raw numbers from a study table. Use "rates" if you already know the proportion of events in each group.
Number of participants in the exposed group who experienced the event.
Number of participants in the exposed group who did NOT experience the event.
Number of participants in the control group who experienced the event.
Number of participants in the control group who did NOT experience the event.
Confidence level for the intervals around relative risk and odds ratio.
Relative Risk (RR)Strong increased risk
2

Risk in the exposed group divided by risk in the control group.

RR confidence interval1.149 to 3.482 (95% CI)
Absolute Risk Reduction (ARR)-0.15%
Relative Risk Reduction (RRR)-1%
Number Needed to Treat (NNT)6.7
Odds Ratio (OR)2.429
OR confidence interval1.211 to 4.870 (95% CI)
P-value (z-test)0.0143
Exposed event rate0.3%
Control event rate0.15%
2 RR
Strong protection<0.5Moderate protection0.5-0.8No effect0.8-1.25Moderate risk1.25-2High risk2+
Exposed rate0.3%
Control rate0.15%

The exposed group had a 100% higher risk than the control group (RR = 2.000).

  • Event rate in the exposed group: 30.0%, compared to 15.0% in the control group.
  • Absolute risk REDUCTION: the exposed group had 15.00 fewer events per 100 people.
  • Number Needed to Treat (NNT): 6.7 - treat 6.7 people to prevent one event.
  • The result is statistically significant (p = 0.014).

Next stepStatistical significance does not equal clinical importance: always interpret the absolute risk difference and NNT alongside the p-value and confidence interval.

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