# Cumulative Incidence Formula Calculator

Determines the probability of developing a disease or studied outcome during the specified time period.

Cumulative incidence, also known as incidence proportion is an epidemiology measure that describes the number of new disease onsets per number of people in the population at risk. This indicator can be measured in cohorts (closed populations only) and requires follow-up of individuals.

Cumulative Incidence = No. of new cases of disease or injury / Size of population at risk x 100

Number of new cases of disease or injury
Size of population at risk
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Steps on how to print your input & results:

2. Then you can click on the Print button to open a PDF in a separate window with the inputs and results. You can further save the PDF or print it.

Please note that once you have closed the PDF you need to click on the Calculate button before you try opening it again, otherwise the input and/or results may not appear in the pdf.

## Cumulative Incidence Explained

Cumulative incidence, also known as incidence proportion is an epidemiology measure that describes the number of new disease onsets per number of people in the population at risk during a specified period of time. This indicator can be measured in cohorts (closed populations only) and requires follow-up of individuals.

CI includes only new cases of disease in the numerator. The denominator is the number of persons in the population at the start of the observation period.

Cumulative Incidence = No. of new cases of disease or injury / Size of population at risk x 100

In contrast to prevalence, incidence is a measure of the occurrence of new cases of disease (or some other studied outcome) during a specified period of time. When reporting incidence, it is important to specify the reported time because, for example, a 5% risk has a different meaning if it is probable in the next 12 months versus the next 5 years.

Whilst the CI may be an easy to understand and facile to use indicator, there are several limitations to it. CI does not distinguish when a disease or other studied outcome occurs during the time period, in some studies being of interest if outcome occurs within several months or years.

CI does not account for competing risks which may result into death of some subjects before observation period ends, meaning it cannot be discerned whether they would have or not developed the outcome of interest during the period, had they not died.

CI requires follow-up of all subjects which, in large scale studies, may be difficult to achieve, with some subjects being “lost to follow-up”.

## References

Centers for Disease Control and Prevention: Principles of Epidemiology in Public Health Practice, Third Edition – An Introduction to Applied Epidemiology and Biostatistics

Specialty: Epidemiology

Article By: Denise Nedea

Published On: October 26, 2020

Last Checked: October 26, 2020

Next Review: October 26, 2025