Association Analysis Performance Measures

This section defines the performance measures used in Association Analysis. Denote the condition item set by X and the consequent item set by Y. Denote an association rule with condition set X and consequent set Y by

Support

Support is the proportion of transactions in which an item set occurs.

Confidence

Confidence is the proportion of transactions that contain the consequent item set, given that the transaction contains the condition item set.

An association rule with a confidence of 0% has a consequent item set that does not appear in any transaction with the condition item set. A confidence of 100% indicates that every transaction that contains the condition item set also contains the consequent item set.

Lift

Lift measures dependency between X and Y.

The numerator for lift is the proportion of transactions where X and Y occur jointly. The denominator is an estimate of the expected joint occurrence of X and Y, assuming that they occur independently.

A lift value of 1 indicates that X and Y jointly occur in transactions with the frequency that would be expected by chance alone. Increasing lift values suggest that Y occurs more often than expected when X is present.