Confidence and Support
Confidence and support are properties of rules. These statistical measures can be used to rank the rules and hence the predictions.
Support: The number of records in the training data set that satisfy the rule.
Confidence: The likelihood of the predicted outcome, given that the rule has been satisfied.
For example, consider a list of 1000 customers (1000 cases). Out of all the customers, 100 satisfy a given rule. Of these 100, 75 are likely to increase spending, and 25 are not likely to increase spending. The support of the rule is 100/1000 (10%). The confidence of the prediction (likely to increase spending) for the cases that satisfy the rule is 75/100 (75%).