In cross-sectional studies, certain characteristics of students at different class levels are measured at the same time, and change is inferred from comparisons. It is clear that any observed freshman-senior difference is affected both by extensity and by intensity— that is, by the number of individuals who change, and by the degree to which each of them changes. The paradigm, though over-simple, illustrates the point that the processes by which change occurs are not the same when mean differences reflect large shifts by a comparatively few individuals and when they represent modest changes by many persons. Movement to a neutral point on an attitude continuum is called neutralization of an attitude, while movement from this point is termed attitude formation. Even though a test scale or questionnaire is designed to measure a single charcteristic, responses to the instrument are never determined by that characteristic alone.