Person-Time Incidence Rate
Calculate a descriptive event rate with an explicit person-time denominator and reporting unit.
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Divide an event count by observed time at risk. Enter aggregate person-time measured in one consistent unit. Defaults are fictional. This tool does not estimate cumulative risk or compare treatment effects.
Calculation results
20 per 1,000 person-years
Rate = 12 ÷ 600 × 1000. Changing the unit label does not convert the entered time; enter the correctly converted denominator yourself.
Define the risk period
For a first-event rate, stop each participant’s time at the first event or the relevant censoring point. For recurrent events, define re-entry and time-at-risk rules; repeated events within one person are correlated. Event counts may exceed participants in a recurrent-event analysis.
A rate is not a percentage. Rates above one event per unit of person-time can be valid. Zero observed events do not establish zero underlying risk. Uncertainty intervals and recurrent-event modeling require additional assumptions and are not calculated here.
Cochrane: effect measures and calculations · Read the practical guide · Download blank worksheet (TXT)