Incidence is defined as which of the following?

Incidence is defined as which of the following?

• A. The number of new cases of an illness per population at risk in a given amount of time
• B. The total number of existing cases at a given time
• C. The proportion of people who die from a disease
• D. The rate of births in a population

Answer: (A)

Incidence is about new occurrences over time. It measures how many fresh cases of a disease arise in a population that is at risk during a specified period, usually expressed per 1,000 or 100,000 person-years. It requires excluding people who already have the disease from the at-risk population. This is different from prevalence, which counts all existing cases at a point in time. The other ideas refer to the total current cases (prevalence), the proportion who die from the disease (case fatality or mortality), or the number of births (birth rate), none of which capture the idea of new cases over time. So the best definition is the number of new cases per population at risk in a given amount of time.

Incidence is about new occurrences over time. It measures how many fresh cases of a disease arise in a population that is at risk during a specified period, usually expressed per 1,000 or 100,000 person-years. It requires excluding people who already have the disease from the at-risk population. This is different from prevalence, which counts all existing cases at a point in time. The other ideas refer to the total current cases (prevalence), the proportion who die from the disease (case fatality or mortality), or the number of births (birth rate), none of which capture the idea of new cases over time. So the best definition is the number of new cases per population at risk in a given amount of time.