ABSTRACT
The individual datum is the unit on which we build to obtain an index, each datum being too specific or too undependable for us to use in studies of the relationships associated with a construct. A dictionary definition of “index” is “a number derived from a series of observations and used as an indicator of a condition; as, an index of intelligence.” English and English (1958, page 258) note that “the term is almost synonymous with variable but is used where it is admitted that quantification is incomplete or imperfect.” This connotation is quite appropriate for most measurement in psychology, especially in personality. The term frequently refers to a score, but “score” has the undesirably narrow connotation of being based on a test. So “index” is used here to refer to a number derived from a series of observations and viewed as representing, to some extent, the degree of a construct (or subconstruct) attributed to a person. Sometimes it will be used collectively to refer to a set of such numbers, one for each of several subjects.
