Rule coverage

The coverage of a rule is the number of cases in the data that are covered by the Left Hand Side of the rule.

The coverage of a itemset is the number of cases in the data that are covered by the attribute values or items specified in the itemset. 

Magnum Opus uses both proportional and count representations of this metric. The coverage count is the raw count of these cases. The coverage proportion is the coverage count divided by the total number of cases in the data.

For instance, suppose that there are 1000 cases and the LHS covers 200 cases. The coverage count is 200 and the coverage proportion is 200/1000 = 0.2.