Calculate the incidence rate (incidence density) per 1,000 or 100,000 person-years, months or days, with an exact Poisson confidence interval.
About this tool
Incidence rate per person-years with an exact Poisson interval.
How to use Person-Time Incidence Rate Calculator
- Enter the number of new cases.
- Enter the total person-time at risk and its unit.
- Choose the multiplier and read the rate with its interval.
Worked example
28 cases over 12,500 person-years is an incidence rate of 2.24 per 1,000 person-years (95% CI 1.49 to 3.24).
When should I use person-time?
When people are followed for different lengths of time, as in most cohort studies, so each person contributes only their time at risk.
How is the confidence interval calculated?
With the exact Poisson method based on the chi-square distribution, which works even for small case counts.
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