Constructing meaningful numerical response when evaluating (dis)comfort perception in a univariate case

In many ergonomic studies, one is interested by the responses of subjects in relation to their environment. The experimental situations are described by geometrical or physical variables, while the subject's responses are recorded frequently by ordered category scales. The critical issue is how to obtain a numerical value for categorical responses. Here, we present a new way of obtaining a numerisation of categorical responses within the general framework of measurement theory. It focuses on the existence of a numerical representation, which can be demonstrated by theorems. Then, the meaningfulness of later numerical statements can be investigated, and a relevant embedding of data can be obtained in numerical and vectorial spaces. This is the case for ordered category scales with the Adams and Messick ‘successive intervals’ method. The method is illustrated by five examples in a univariate situation. The proposed method is also compared with three usual numerical scales in ergonomics.