1. What is Cumulative Incidence?

Cumulative Incidence (CI) is a measure of disease frequency that represents the proportion of a population that develops a disease during a specified period. It estimates the probability or risk of individuals developing the disease during that time.

2. How Does the Calculator Work?

The calculator uses the cumulative incidence formula:

Where:

• \( \text{New Cases} \) — Number of new disease cases during the time period
• \( \text{Population at Risk} \) — Number of people at risk of developing the disease at the beginning of the period

Explanation: The result is typically expressed as a proportion but can be multiplied by 100 to present as a percentage.

3. Importance of Cumulative Incidence Calculation

Details: Cumulative incidence is crucial in epidemiology for measuring disease risk, comparing disease occurrence across populations, identifying risk factors, and evaluating prevention strategies.

4. Using the Calculator

Tips: Enter the number of new cases and the population at risk. Both values must be positive integers, and new cases cannot exceed the population at risk.

5. Frequently Asked Questions (FAQ)

Q1: What's the difference between incidence rate and cumulative incidence?
A: Cumulative incidence measures the proportion of people who develop disease during a period, while incidence rate measures how quickly disease occurs in a population (cases per person-time).

Q2: What time period should I use for cumulative incidence?
A: The time period should be clearly specified (e.g., 1-year cumulative incidence) as the value depends on observation duration.

Q3: Can cumulative incidence exceed 1 (or 100%)?
A: No, since it represents a proportion of the population, it ranges from 0 to 1 (0% to 100%).

Q4: What if people leave the study population during the observation period?
A: For accurate cumulative incidence, the population should be fixed (no new entries/exits) or statistical methods like Kaplan-Meier should be used.

Q5: When is cumulative incidence most appropriate?
A: It's best for fixed populations with complete follow-up and when the disease of interest is uncommon.