Overview
This lecture explains the key differences between the epidemiological terms "incidence" and "prevalence," using examples to clarify their meanings.
Incidence
- Incidence refers to the number of new cases of a disease that develop during a specific time period.
- It answers the question: "How many people got the disease during this time?"
- Incidence is always measured in relation to a time frame (e.g., cancer cases in 2019).
- Example: Approximately 40,000 Americans get HIV each year, so the incidence of HIV in 2019 is around 40,000.
Prevalence
- Prevalence is the total number of people who currently have a disease at a specific point in time.
- It includes both new cases (from the current time period) and existing cases (from previous years).
- Prevalence answers: "How many people have this disease right now?"
- Example: The total number of Americans living with HIV in 2019 includes everyone diagnosed in previous years and still alive with the disease.
- Prevalence is always equal to or higher than incidence because it includes all existing cases.
Key Terms & Definitions
- Incidence — The number of new disease cases occurring in a defined population during a specified time period.
- Prevalence — The total number of disease cases (both new and existing) present in a population at a given time.
Action Items / Next Steps
- Review the definitions and differences between incidence and prevalence.
- Prepare examples of diseases to practice identifying incidence and prevalence.