\begin{equation}
S_d = \frac{\sum_{t=1}^{d}\sum_{i=1}^{N_t} p(h_{i,t}) - \sum_{t=1}^{d}\sum_{i=1}^{N_t} n(h_{i,t})}{\sum_{t=1}^{d}\sum_{i=1}^{N_t} p(h_{i,t}) + \sum_{t=1}^{d}\sum_{i=1}^{N_t} n(h_{i,t})} 
\end{equation}
