One of the central issues of research is making an appropriate comparison. Results from a treatment are meaningless by themselves. To have meaning, they must be compared to something. Knowing that a student got 10 items correct on a test tells us nothing unless we have some context for comparison; that context could be a mastery criterion, the student’s performance on a pretest, the performance of similar students, and so on. Each of these kinds of comparisons gives different kinds of meaning to the raw score.