Precision is the number of correct fills divided by the total number generated by the system, and recall is the number of correct fills divided by the the total number in the key: In the example, there are 8 correct fills, 13 generated fills, and 15 possible fills in the key, resulting in a precision of 0.615 and a recall of 0.533.
this is a substantial reduction from the F-score of 0.571 that the overgenerated event actually receives, a change which implicitly instructs the developer to remove the rules responsible for extracting the correct event.