An index that measures the number of individuals who have become ill because of a specific disease within a susceptible population during a specific period is called the

• A. Prevalence rate
• B. Morbidity rate
• C. Mortality rate
• D. Incidence rate

Answer: (B)

Morbidity rate captures how often illness occurs in a population over a specific time. It focuses on the occurrence of disease-related illness among people who are at risk during that period, which is exactly what the statement describes: new illness events within a susceptible group over a defined time frame. This helps quantify the burden of disease in the community and track how illness levels change over time.

Prevalence would count all existing cases at a point or period, not just new ones; mortality relates to deaths; incidence rate specifically refers to new cases per population at risk, but the term that best fits the idea of illness occurrence in the population over time is morbidity rate.