From: Buying electricity resilience: using backup generator sales in the United States to understand the role of the private market in resilience
SAIFI = \(\frac{{\sum }_{i=1}^{n}{N}_{i}}{{N}_{T}}\)
SAIDI = \(\frac{{\sum }_{i=1}^{n}{{r}_{i}N}_{i}}{{N}_{T}}\)
CAIDI = \({\sum }_{i=1}^{n}\frac{{{r}_{i}N}_{i}}{{N}_{i}}\)