We expect an increase in the future number of cases, if \(EVI_{t-1,t}\) exceeds a threshold \(c\) \(\left(c\in\left[0,1\right]\right)\) and the observed cases at time point \(t,\left(y_t\right)\) are higher than the average of the reported cases in the previous week:
\[Ind_{EVI_{t-1,t}} = \begin{cases} 1 \;\;\; if \;\;\; EVI_{t-1,t} \geq c \;\; \wedge \;\; y_t \geq \overline{\mu}_{t:t-7} \\ 0 \;\;\; \text{otherwise} \end{cases} \]