Interval scales are often referred as “equal interval scales.” Consequently a) the rank ordering of objects on an attribute is known, b) the distances among objects on the attribute are also known, but c) the absolute magnitudes of the attribute are unknown. Deviation from any mean can be calculated without actually knowing how far anyone is from the zero point (Nunnally and Bernstein, 1994).
Transformations are restricted because the relative sizes of the distances between values contain meaningful information. However, the only transformation that will retain the information contained in the original set of values is of the form in which A and B are constants: y = Ax + B. A set of values such as 4,5,3,2 could be transformed into 9, 11, 7, 5 by the transformation y = 2x + 1 with no loss of information under the construct study (Crocker
, 1984, p.48).