When analyzing the trend of an epidemic, it is important to distinguish between “forecast”, “scenario analysis” and “projection”. In thefocus on the website of the Istituto Superiore di Sanità you can find the respective definitions and explanations, published in collaboration with Fondazione Bruno Kessler. “We drafted this note”, explains epidemiologist Stefano Merler, who directs the Health Emergencies Center at FBK, “to clarify the use of mathematical models in the study of epidemics, and in COVID-19 in particular. In fact, mathematical models, unlike what is probably common belief, are not only used to make predictions and certainly are not used primarily for making predictions. Especially with COVID-19, whose degree of predictability is extremely low. These are tools mainly used for analyzing the trend of the epidemic, for estimating parameters that cannot be estimated in any other way, for evaluating the effectiveness of possible intervention strategies. All things, together with many others that can be investigated with models, which help us to better understand the epidemic we are facing” You can find the definitions explained by the Italian Institute of Helath (ISS) and Fondazione Bruno Kessler below.