How is cumulative incidence calculated?

Cumulative incidence is a measure used in epidemiology to determine the occurrence of new cases of a disease in a specific population over a certain period of time. It is calculated by taking the total number of new cases of the disease that arise in a population during that period and dividing it by the population at risk of developing the disease at the beginning of the study period.

The reason why the correct choice emphasizes "total new cases divided by population at risk" is that it focuses specifically on the subset of the population that is susceptible to the disease. This approach provides a clearer understanding of the risk of disease within that group. It sets the stage for interpreting how common the disease is among those who could potentially contract it, distinguishing it from overall population figures that might include those who are not at risk.

In contrast, dividing total cases by total population does not accurately reflect the situation since it includes individuals who may not have been at risk for the disease and could lead to misleading interpretations. Similarly, total deaths divided by total cases focuses on mortality rather than new incidences of the disease, while total recoveries divided by total population also misrepresents the concept by mixing recovery outcomes with the total population without regard for initial risk. This specificity is crucial for assessing the dynamics