Which statement correctly defines prevalence and incidence?

• A. Prevalence is the rate of new cases; incidence is the proportion of people with a condition at a given time.
• B. Prevalence is the proportion of people with a condition at a given time; incidence is the rate of new cases over a period.
• C. Prevalence equals the lifetime risk; incidence equals the annual risk.
• D. Prevalence excludes existing cases and focuses on risk; incidence includes them.

Answer: (B)

Prevalence vs incidence describe how we measure disease in a population. Prevalence is the proportion of people who have the condition at a specific moment (or over a defined period) and shows how widespread the disease is at that time. Incidence is the rate at which new cases occur during a defined time interval, usually expressed as new cases per population per time.

This aligns with the statement that prevalence is the proportion of people with the condition at a given time, and incidence is the rate of new cases over a period. Remember, prevalence reflects both how common the disease is and how long people live with it, while incidence focuses on new occurrences over time. For example, if 100 of 1,000 people have the disease at a snapshot, prevalence is 10%. If 20 new cases develop over a year among those at risk, the incidence rate describes that new flow of cases per year.