ABSTRACT
Most analyses of physics assessment tests have been done within the framework of classical test theory in which only the number of correct answers is considered in the scoring. In the 1980s, physics educators started to probe students’ conceptual understanding of physics concepts. It was found that a student’s response not only depends on his or her educational history (i.e., previous experience or preexisting knowledge about a specific concept), but also depends on the student’s cognitive processes at the particular instant they are triggered by a particular question presented. This suggests that in at least some cases a student can be thought of as being in a mixed-model state; that is, they can be thought of as simultaneously occupying a number of distinct model states or (possibly incompatible) characteristic ways of thinking about a problem-and which state would be invoked to solve a particular question depends on the features of that question.
