Calculating _____ relates the number of identified cases to the population at risk.

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

Answer: (D)

Incidence measures new cases in a population at risk over a defined period. It ties the count of people who develop the disease to the number of people who could possibly develop it, giving a sense of risk during that time frame. The population at risk excludes those who already have the disease or are immune, which is why incidence specifically reflects the rate at which new cases arise.

Prevalence, by contrast, counts all existing cases at a point in time or over a period, so it reflects both how common the disease is and how long people live with it, not the rate of new development. Attack rate is similar to incidence but is typically used for a specific, defined group during an outbreak and over a short period. Mortality rate relates deaths to the population, not disease occurrence.

So the blank is filled best by incidence.