ABSTRACT
A huge number of situations can be described by the following abstract framework. Each of a set of objects is known to belong to one of two classes. An assignment procedure assigns each object to a class on the basis of information observed about that object. Unfortunately, the assignment procedure is not perfect: errors are made, meaning that sometimes an object is assigned to an incorrect class. Because of this imperfection, we need to evaluate the quality of performance of the procedure. This might be so that we can decide if it is good enough for some purpose, attempt to improve it, replace it with another procedure, or for some other reason.
