EVI is based on the calculation of the rolling standard deviation for a time series of epidemic data (i.e. the number of new cases per day). The number of consecutive observations used for this calculation, per rolling window, is the rolling window size – \(m\). At each time step, for a rolling window of size \(m\), the observations within the window are obtained by shifting the window forward, over the time series data, one observation at a time (Figure 1).