ABSTRACT
Tests have many different purposes. They can be used (a) to develop a description of a person’s capabilities; (b) to search for an explanation for a person’s level of performance; (c) to facilitate the adaptation of training to a particular person’s capabilities; (d) as a screening device to warn about a student’s lack of progress in learning a skill; or (e) to choose which of a set of people should be given a specific task. For some of these purposes, a global quantitative characterization is appropriate; for example, if we want only to be warned of any students who lag behind their peers in school, we can give a global achievement test and look for outlier scores. For other purposes, qualitative details are needed if a test is to be useful; for example, if a student has incomplete or incorrect knowledge that has led to systematic misconceptions, it is much more useful to know about the nature and basis of those misconceptions than simply to know that the student is not performing well on problems we wish he or she could solve.
