Constrained and confirmatory multidimensional scaling (MDS) are not equivalent. Constraints refer to the translation of either theoretical or data analytical objectives into computational specifications. Confirmation refers to a study of the balance between systematic and random variation in the data for modeling of the systematic part. Among the topics discussed from this perspective are the role of substantive theory in MDS studies, the type of constraints currently envisaged, and the relationships with other data analysis methods. This paper points out the possibility of using either sampling models or resampling schemes to study the stability of MDS solutions. Parallel to Akaike's (1974) information criterion for choosing one out of many models for the same data, a general stability criterion is proposed and illustrated, based on the ratio of within to total spread of configurations issued from resampling.
Scaling Analysis and OptimizationThe coupling of constraints and scaling, although not new, is still extremely vital. The first modem scaling model, developed by Thurstone (e.g., 1927), immediately entailed the necessity of a judicious choice of constraints, as classified in the five famous 6bc~sese&dquo; These were internal constraints in the sense that the modified model would still accommodate the same set of observations, possibly less accurately, but with more predictive value. Guttman (1946) took a number of important additional steps. He showed that Thurstone's s method, relying on an underlying multivariate normal distribution, could be replaced by an approach in which the optimization of a goodness-of-fit function is the central concept. This was an extension of similar developments occurring at that time in test theory and in contingency table analysis (for current reviews, s~e l~lishisato, 1980, and Gin, 1981) to the scaling of paired comparison and rank order data. Moreover, Guttman showed that introducing an additional type of constraint was not a problem. The proper objective would be to find scale values for the stimulus objects that are &dquo;best able to reproduce the judgment of each person in the population on each comparison&dquo; (Guttman, 1946, p. 14~) and that are also perfectly linearly predictable from a predeterrrgined set of (design) variables.Although through hindsight it seems clear that it would have been possible to formulate a constrained multidimensional scaling (MDS) method within Guttman's framework, the early paradigm for MDS was to split the problem into two distinct steps. From the very first published psychometric application by Klingberg (1941)-based on earlier work by Richardson (1938)-to the authoritative presentation in Torgerson's (1958) book, it is evident that the main burden and first step of the analysis was to find a one-dimensional scale of psychological distances between pairs of stimulus objects. This was usually done by any of the varat UNIVERSITE DE MONTREAL on June 23, 2015 apm.sagepub.com Downloaded from