This paper is concerned with the scaling method of "ratio estimation." The simple theory that equates reported ratio judgments to ratios of psychological magnitudes is first considered, then two close relatives of this theory are formulated, each of which places weaker constraints on the structure of the data. Structural conditions are stated that express the relations that must hold among observed ratio judgments for each of the models. The models proposed are "cumulative" in the sense that the second is a weakened version of the first, and the third a weakened version of the second. A special feature of the models is that they may be tested entirely in terms of observables, avoiding the necessity of scale construction prior to testing. Tests were carried out on data from 9 published studies. The strongest model, typically used in scale construction using ratio estimation data, was generally inadequate, showing large systematic errors. However, the weakest version generally passed the tests of internal consistency, and the model equation provided a basis for constructing ratio scales utilizing bias parameters.This paper is concerned with the scaling method of ratio estimation. In a typical task, a pair of stimuli (a, b) is presented, and the subject is instructed to respond with a number that corresponds to the sensation "ratio" of a to b relative to a defined attribute. In another variation, called "free ratio estimation" (Mashhour, 1964), subjects assign a number to each of the two stimuli such that the ratio of the numbers assigned reflects the sensation ratio. Thus the method applies to any response that can be transformed to a ratio. The method does not require a modulus, and usually all possible pairs are presented.The method of ratio estimation has a long history (Ekman, 1958;Stevens, 1958), but recently the simple theory that equates the reported sensation ratio to a ratio of psychological magnitudes has been questioned (e.g., Fagot, Stewart, & Kleinknecht, 1975;SjOberg, 1971). If the simple theory does not lead to valid ratio scales, how might the theory be modified without abandoning the basic assumption that subjects are capable of making ratio judgments that are consistent in a well-defined sense?This paper answers the question by developing two close relatives of the simple theory of ratio estimation that place weaker constraints on the structure of the data. The different versions constitute a theory of relative judgment in the obvious sense that a stimulus is judged relative to another stimulus. This relativity is in no sense trivial, since it leads to the formulation of tests of internal consistency not possible with methods such as the pure form of magnitude estimation in which stimuli are judged one at a time.Work on this paper was carried out, in part, during the author's tenure as a Fellow at the Netherlands Institute for Advanced Study, Wassenaar, Holland.
243The basic question asked is: Assuming that a ratio scale exists, what relations must hold among observed ratio estimations? The answe...