Manipulability, unanimity, anonymity and merging functions

A merging (or assessment aggregation) function (see 7]) is a rule that synthesizes several individual assessments, or numerical judgements, by creating a unique “collective” assessment. Individual i can manipulate assessment aggregation if the change in the merged assessment due to a change in i's assessment from x to y depends solely on x and y. Some assumptions on the functional form capturing this dependence are put forward and their effects on aggregation investigated under unanimity and anonymity conditions using a functional equation approach. Attention is restricted to three types of results: the merging function does not exist; it is the arithmetic mean; it is dictatorial. Received: 21 November 1997/Accepted: 31 May 1999