A law of comparative judgment

A new psychological law, called the law of comparative judgment, is presented with some of its special applications in the measurement of psychological values. This law is applicable not only to the comparison of physical stimulus intensities but also to qualitative comparative judgments, such as those of excellence of specimens in an educational scale. It should be possible also to verify it on comparative judgments which involve simultaneous and successive contrast. The law is stated as follows:[Equation omitted]in which S1 and S2 are the psychological scale values of the two compared stimuli; x12 is the sigma value corresponding to the proportion of judgments p1 > p2. ς1 is the discriminal dispersion of stimulus R1 and ς2 is the dispersion of stimulus R2. r is the correlation between the discriminal deviations of R1 and R2 in the same judgment. This law is basic for work on Weber's and Fechner's laws, applies to the judgments of a single observer who compares a series of stimuli by the method of paired comparisons when no "equal" judgments are allowed, and is a rational equation for the method of constant stimuli. The law is then applied to five cases each of which involves different assumptions and different degrees of simplification of the law for practical use. The weighting of the observation equations is discussed because the observation equations obtained with the five cases are not of the same reliability and hence should not be equally weighted. (APA PsycInfo Database Record (c) 2016 APA, all rights reserved)