What is the Classification Success Index?
The Classification Success Index (CSI) is a (fairly uncommon) measure for evaluating classifiers. The CSI focuses exclusively on the positive class. It is calculated as follows:
The terms (1-PPV) and (1-TPR) correspond to the proportions of type I and type II errors. The measure ranges from -1 to 1. A value of -1 means that all predictions are false positives or false negatives — the predictions are inverted. A value of 1 means the predictions are perfect. A value of 0 is the result of random predictions.
Because of the focus on the positive class, it might not be the best measure to assess models in situations of severe class imbalance.