How is incidence rate defined?

• A. The number of new cases in a population during a period, divided by the population at risk
• B. The number of new health-related events or cases in a population exposed to risk during a specific period of time, divided by the total population
• C. The total number of cases in the population during the period divided by the population at risk
• D. The rate of recovery in the population over time

Answer: (B)

Incidence rate measures how quickly new cases appear in a population that is at risk over a defined period. The best choice captures counting those new health-related events or cases that occur among people exposed to risk during a specific time, and then relating that count to the population at risk during that period. This highlights the time‑bound nature of new occurrences and excludes people who are not at risk (or who already have the condition). It’s different from prevalence, which counts all existing cases at a point in time, and from recovery rate, which looks at how quickly people recover rather than how many new cases arise.