Evaluating performance of binary classification systems

A computer program product for evaluating a binary classification system, the binary classification system being operable to classify each of a plurality of events as a first event type or a second event type, at least some of the events of the first event type, but none of the second type, being independently verifiable with reference to verification data, the binary classification system being susceptible to a first error type in which events of the first event type are classified as the second event type, and a second error type in which events of the second event type are classified as the first event type, the computer program product comprising at least one non-transient computer-readable medium having computer program instructions stored therein operable when executed by at least one computer to evaluate operation of a first configuration of the binary classification system with reference to an objective function, the objective function having been derived by expressing a number of errors of the second error type exclusively in terms of a number of errors of the first error type with reference to the verification data, and by assuming relative proportions of the first and second event types within the plurality of events, the objective function having been further derived with reference to a first cost associated with making errors of the first error type and a second cost associated with making errors of the second error type, and wherein the first and second costs are assumed to be substantially the same.