Modelling ordinal preferences and consensus

Various models have been developed for representing ordinal preferences and aggregating voter responses to derive a consensus. The early applications of ordinal models were found in the area of preferential voting. Recently they have been used for ranking investment options, R&D options, R&D projects, etc. A review is given a set of consensus models for problems where ordinal data is present. These models are compared and contrasted in terms of their mathematical bases, and in terms of the frequency with which they result in the same consensus of opinions.