ABSTRACT
At the nominal scale level, a difference tells us whether two scores, that is, two labels, are the same. The magnitude of a difference cannot be interpreted. The decision is only between equal or different. At the ordinal level, a difference tells us how many ranks apart two objects are. The magnitude of the difference can be interpreted only in the sense that it counts the number of ranks that separate two objects. The same number of ranks between pairs of objects can correspond to different distances (if these are defined). At the interval level, a difference tells us how many units apart two objects are, and the units are the same across the entire range of admissible scores. The same holds true for the ratio scale level.
