CAIFI

The Customer Average Interruption Frequency Index (CAIFI)<ref>Yeddanapudi, Sree. "Distribution System Reliability Evaluation". Iowa State University. Archived from the original on 26 December 2011. Retrieved 18 June 2011.</ref> is a popular reliability index used in the reliability analysis of an electric power system.<ref>Power Distribution Planning Reference Book, H. Lee Willis, published by CRC Press, 2004, page 112</ref> It is designed to show trends in customers interrupted and helps to show the number of customers affected out of the whole customer base.

<math>\mbox{CAIFI} = \frac{\mbox{Total Number of Customer Interruptions}}{\mbox{Number of Distinct Customers Interrupted}}</math>