Which statement best describes incidence versus prevalence?

• A. Incidence measures all existing cases at a point in time or over a period
• B. Incidence measures new cases over a period; prevalence measures all existing cases at a point in time or over a period
• C. Incidence is about mortality; prevalence about morbidity
• D. Incidence equals prevalence

Answer: (C)

The main idea is distinguishing how we count disease in a population: new cases versus all existing cases. Incidence focuses on new occurrences of the disease in a defined population over a specified time, telling you how fast people are developing the condition. Prevalence, by contrast, counts everyone who already has the disease at a given moment (point prevalence) or during a defined period (period prevalence), showing how widespread the disease is.

This distinction matters because incidence reflects risk and the rate of new events, while prevalence reflects the overall burden of disease, influenced by how long people stay ill, recover, or die. Mortality relates to deaths, and morbidity relates to illness burden, but neither by itself describes how often new cases occur or how many people are living with the condition at a given time.

So the correct framing is that incidence measures new cases over a period, and prevalence measures all existing cases at a point in time or over a period.