Chapter 5. Evaluating Classification and Predictive Performance

In this chapter we discuss how the predictive performance of data mining methods can be assessed. We point out the danger of overfitting to the training data and the need for testing model performance on data that were not used in the training step. We discuss popular performance metrics. For prediction, metrics include Average Error, MAPE, and RMSE (based on the validation data). For classification tasks, metrics include the classification matrix, specificity and sensitivity, and metrics that account for misclassification costs. We also show the relation between the choice of cutoff value and method performance, and present the receiver operating characteristic (ROC) curve, which is a popular plot for assessing method performance at different cutoff values. When the goal is to accurately classify the top tier of a new sample rather than accurately classify the entire sample (e.g., the 10% of customers most likely to respond to an offer), lift charts are used to assess performance. We also discuss the need for oversampling rare classes and how to adjust performance metrics for the oversampling. Finally, we mention the usefulness of comparing metrics based on the validation data to those based on the training data for the purpose of detecting overfitting. While some differences are expected, extreme differences can be indicative of overfitting.

Introduction

In supervised learning we are interested in predicting the class ...

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