This view reflects a scaling tradition with close connections to Rasch measurement. Although Thorndike does not calibrate individuals and items onto an underlying latent variable scale simultaneously, he does attempt to develop calibrated scales that can be used to measure individuals. Wood's third principle, that the function to be measured must be defined as adequately as possible, deals primarily with content validity. Consistency is defined by Thorndike and Wood as the unidimensionality of a scale. Wood recommends inspecting test items in order to determine the consistency of the test, but, in his view, useful test scores can be obtained from any hodgepodge of combinations of items measuring visibly different content areas, such as reading and mathematics.
Comparability deals with what constitutes a useable scale.
But Wood's discussion of this principle is disjointed and difficult to understand because the test score tradition does not contain the concept of a calibrated item scale. Within Thorndike's scaling tradition, however, the idea of comparisons is fundamental. Items are calibrated through a comparison process, and the measurement of individuals is viewed as a comparison between an individual's ability and item difficulties on a latent variable scale. Thorndike's and Wood's theories of measurement offer important insights into major measurement problems identified in the first quarter of this century. Laudan L 1977.