EVI is calculated for a rolling window of time series epidemic data (i.e. the number of new cases per day). At each step, the observations within the window are obtained by shifting the window forward over the time series data one observation at a time.
Let \(x_i=\left\{x_1,\ x_2,...,x_n\right\}\) be a time series of length \(N\). The rolling window size - that is the number of consecutive observations per rolling window - is \(m\). With \(0<m\le m_{\max}\) and \(0<m_{\max}\le N\), there are \(t=N-m+1\) consecutive rolling windows.