Which statement correctly defines incidence and prevalence?

• A. Incidence is the total number of existing cases at a point; prevalence is new cases over time.
• B. Incidence is new cases in a population over a period; prevalence is the total number of existing cases at a point or over a period.
• C. Incidence is the proportion of the population that died from a disease; prevalence is the proportion cured.
• D. Incidence is the rate of recovery; prevalence is the rate of onset.

Answer: (B)

Incidence versus prevalence fundamental idea: incidence measures the rate of new disease appearances in a population over a specified time, while prevalence measures how widespread the disease is by counting all existing cases at a given time (point prevalence) or over a period (period prevalence). The statement that incidence is new cases over a period and prevalence is the total number of existing cases at a point or over a period correctly captures these definitions. The other options mix up these concepts or refer to outcomes like death or cure, or to unrelated ideas like recovery rate, which are not how incidence and prevalence are defined.