Introduction: Classification and prediction methods can be compared and evaluated according to the following criteria:
Accuracy: The accuracy of a classifier refers to the ability of a given classifier to correctly predict the class label of new or previously unseen data (i.e., tuples without class label information). Similarly, the accuracy of a predictor refers to how well a given predictor can guess the value of the predicted attribute for new or previously unseen data. Accuracy measures are given in Section 6.12. Accuracy can be estimated using one or more test sets that are independent of the training set. Estimation techniques, such as cross-validation and bootstrapping. Strategies for improving the accuracy of a model are given in Section 6.14. Because the accuracy computed is only an estimate of how well the classifier or predictor will do on new data tuples, confidence limits can be computed to help gauge this estimate.
Speed: This refers to the computational costs involved in generating and using the given classifier or predictor.
Robustness: This is the ability of the classifier or predictor to make correct predictions given noisy data or data with missing values.
Scalability: This refers to the ability to construct the classifier or predictor efficiently given large amounts of data.
Interpretability: This refers to the level of understanding and insight that is provided by the classifier or predictor. Interpretability is subjective and therefore more difficult to assess. We discuss some work in this area, such as the extraction of classification rules from a “black box” neural network classifier called back propagation (Section 6.6.4).
These issues are discussed throughout the chapter with respect to the various classification and prediction methods presented. Recent data mining research has contributed to the development of scalable algorithms for classification and prediction. Additional contributions include the exploration of mined “associations” between attributes and their use for effective classification.
