Describes a classroom demonstration that illustrates the error of using an inappropriate test to conclude that a specific ability does not exist within a subject or a population. Shows ways to expand the lesson to cover the issue of null conclusions. Points out social and methodological implications of the demonstration. (Author/LS)

Multidimensional item difficulty (MID) is proposed as a means of describing test items which measure more than one ability. With mathematical story problems, for instance, both mathematical and verbal skills are required to obtain a correct answer. The proposed measure of MID is based upon three general assumptions: (1) the probability of…