Population at risk refers to:

Population at risk refers to:

• A. The group of individuals who are already diseased at the start.
• B. The entire population, regardless of risk status.
• C. The number of cases of disease in the population.
• D. The group of individuals who are susceptible to developing the disease and are observed for the outcome.

Answer: (D)

Population at risk means the people who could actually develop the disease during the study because they are free of it at the start and are susceptible to it. Only this group can contribute new (incident) cases over time, which is why it serves as the appropriate denominator for incidence measurements. It excludes those who already have the disease or who are not susceptible, and it can change as people develop the disease or become lost to follow-up. In other words, counting everyone regardless of risk would mix those who cannot get new disease with those who can, distorting the rate. For example, if 50 people already have the disease at baseline in a cohort of 1,000, the population at risk for new cases would be the remaining 950 observed individuals who could develop the disease.

Population at risk means the people who could actually develop the disease during the study because they are free of it at the start and are susceptible to it. Only this group can contribute new (incident) cases over time, which is why it serves as the appropriate denominator for incidence measurements. It excludes those who already have the disease or who are not susceptible, and it can change as people develop the disease or become lost to follow-up. In other words, counting everyone regardless of risk would mix those who cannot get new disease with those who can, distorting the rate. For example, if 50 people already have the disease at baseline in a cohort of 1,000, the population at risk for new cases would be the remaining 950 observed individuals who could develop the disease.