Of the following statement(s), which is/are correct?
1. Incidence is the number of new cases of disease occurring in a defined population during a specified time.
1. Prevalence is the number of old cases existing at a given point of time.
1. Prevalence depends upon the incidence and duration of illness.
Choose the most appropriate answer from the options given below:

Correct option is D

Incidence refers to new cases of a disease in a population over a specified time, reflecting the risk of developing disease. Prevalence, on the other hand, includes both old and new cases at a particular point or over a period — so option 2 is partially incorrect if interpreted strictly as “old cases.” The relationship between incidence and duration affects prevalence: Prevalence = Incidence × Duration.
Explanation for each option:
1. Correct. Incidence captures new cases and is used in outbreak and trend analysis.
1. Incorrect. Prevalence includes both old and new cases — not just old ones — making this statement inaccurate.
1. Correct. Prevalence rises if incidence or disease duration increases, and falls when either decreases or recovery/death occurs quickly.