Final answer:
Population at risk is essential for describing events in a population because it allows us to measure disease frequency, assess risk and impact, and predict future changes.
Step-by-step explanation:
Population at risk is essential for describing events in a population because it allows us to identify the individuals who are susceptible to a disease or condition. By defining the population at risk, we can accurately measure the frequency of disease, assess the risk and impact of the disease, and predict future changes in the population. For example, in epidemiology, population at risk helps in determining the incidence and prevalence rates of a disease. It also helps in identifying risk factors and developing appropriate public health interventions