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Performance Metrics: Classification Success Index

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:

CSI = 1 - (1 - PPV + 1 - TPR) = PPV + TPR - 1

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.

Further reading: