ABSTRACT
Chapter 1 discussed the inevitable imperfection of any single measure as an operationalization of a theoretical concept and the consequent need for multiple operationism. The translation between an abstract theoretical conception and its operational realization is always incomplete. Even so, although all translations (i.e., measures) are imperfect, individual measures vary in the adequacy with which they characterize the underlying conceptual variable of interest. Some measures come closer than others to representing the true value of the concept, in part because they are less susceptible to sources of systematic error or random fluctuation. The quality of a given measure is expressed in terms of its reliability and validity. Briefly, reliability is the consistency with which a measure assesses a given concept; validity refers to the degree of relationship, or the overlap, between an instrument and the construct it is intended to measure.
