Disease Incidence Rates
Calculate incidence rates, cumulative incidence, and attack rates for epidemiological studies. Essential for outbreak investigation and disease surveillance.
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Rate for varying follow-up Cumulative for fixed cohort Attack rate for outbreaks
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Why: Incidence measures how quickly disease occurs in a population. Critical for outbreak investigation, surveillance, and public health planning.
How: Incidence rate = new cases ÷ person-time. Cumulative incidence = new cases ÷ population at risk. This calculator supports both approaches with confidence intervals.
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Sample Epidemiological Scenarios
📈 Disease Occurrence Data
⚙️ Calculation Options
For informational purposes only — not medical advice. Consult a healthcare professional before acting on results.
🏥 Health Facts
Incidence rate = cases per person-time
— Epidemiology
📊 What is Incidence Rate?
Incidence rate (also called incidence density or person-time incidence rate) measures the frequency of new disease cases occurring in a population over time. It is a fundamental measure in epidemiology used to understand disease dynamics, compare populations, and evaluate interventions.
Unlike prevalence (which measures existing cases), incidence specifically counts NEW cases, making it essential for understanding disease transmission, identifying risk factors, and tracking epidemic curves.
Key Concepts:
- Cumulative Incidence: Proportion of at-risk population developing disease
- Incidence Rate: Number of new cases per person-time at risk
- Attack Rate: Cumulative incidence during an outbreak
- Person-Time: Sum of time each person was at risk
📋 How to Calculate Incidence Rate
Cumulative Incidence:
Also called "risk" - proportion who develop disease during time period
Incidence Rate:
Accounts for varying follow-up times in cohort studies
⏰ When to Use Incidence Rate
Use For:
- ✓ Outbreak investigations
- ✓ Disease surveillance programs
- ✓ Cohort study analysis
- ✓ Comparing populations
- ✓ Evaluating interventions
- ✓ Cancer registry reporting
Examples:
- • COVID-19 weekly case rates
- • Annual cancer incidence
- • Flu attack rates
- • Hospital infection rates
- • Vaccine trial endpoints
📐 Incidence Rate Formulas
Cumulative Incidence (Risk):
CI = Number of New Cases / Population at Risk at Start
Incidence Rate (Density):
IR = Number of New Cases / Total Person-Time at Risk
95% Confidence Interval (Poisson):
CI = Rate ± 1.96 × sqrt(Cases) / Person-Time × Multiplier
Attack Rate:
AR = (Cases in outbreak / Exposed population) × 100%
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