Graphical representation of the Epidemic Volatility Index (EVI) model. \(T\) denotes the end of the time series, \(t\) a time point of the time-series. \(Se\) and \(Sp\) stand for the sensitivity and specificity of the testing procedure calculated at each step of the algorithm. Solid lines are explanatory; at each time point dashed lines represent the iterative optimization process while the bold solid line denotes the end of the algorithm.