At each of the \(t\) steps, \(EVI\) uses the standard deviation \(\left(s_t\right)\) of the newly reported cases \(\left(y_{j_t}=\left\{y_{1_t},\ y_{2_t},...\ ,y_{m_t}\right\}\right)\) within the specified \(m\)\[s_t=\sqrt{\frac{1}{m}\sum_{i_t=1}^m\left(x_{i_t}-\overline{x}_t\right)^2}\]