Once an outbreak starts, it is important to quantify how a disease is spreading, how it is affecting the population, and how different public health measures will have an impact on its effects. Epidemiology is the study of how a disease is distributed in a population, and of the different factors that determine this distribution. These studies can help to quantify the main population factors that led to the introduction and spread of an infectious disease in the population and the conditions that are associated with the severity of the disease. Epidemiology can also be used to assess the current extent of the disease and the effectiveness of different interventions, including different therapies and public health measures. Finally, it can also help to make predictions on likely future scenarios, given the current assessment of the situation and the different measures taken.