Final answer:
Incidence measures the rate of new occurrences, while prevalence measures the total number of existing cases of a disease. Prevalence is used for healthcare planning, and incidence is used to assess the effectiveness of interventions.
Step-by-step explanation:
Incidence and prevalence are two important measures of disease frequency in epidemiology. Incidence measures the rate of new occurrences or onset of a disease within a population during a specific period, while prevalence measures the total number of existing cases of a disease or condition within a population at a specific point in time. We might want to use prevalence when planning healthcare resources for managing and treating existing cases, and incidence when assessing the effectiveness of interventions or preventive measures in reducing the occurrence of a disease.