Ennis, Mullen and Frijters (1988) derived a unidimensional Thurstonian scaling model for Richardson's method of triads so that the results could be scaled under normality assumptions about the item percepts.
In 1988, Ennis, Mullen, and Frijters created a one-dimensional Thurstonian scaling model based on Richardson's triad method, allowing for the analysis of data under the assumption of normal distribution for the item perceptions.