Modelling scale effects and uncertainty in rating surveys

In social and behavioural sciences the optimal use of rating scales is an important issue. Discussions on the number of response categories that optimizes the psychometric proprieties of the scales and sums up the global amount of information deriving by the response patterns are the aim of several studies. In a parametric context, this paper faces two specific topics: verify if the number of modalities affects the interpretation of responses and suggest a transformation of the observed ratings distribution when a comparison of results with a different numbers of response categories is necessary. Analysis is carried out within the statistical framework introduced for the study of feeling and uncertainty components in the process of responses which generate ordinal scores. Some empirical evidences and a simulation experiment support the usefulness of the approach.