 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.MaxDiff may involve multidimensional percepts, unlike most-least models that assume a unidimensional representation.MaxDiff and most-least methods belong to a class of methods that do not require the estimation of a cognitive parameter as occurs in the analysis of ratings data.