Coalitional manipulability of three scale evaluative voting: Quantification and comparison with three other voting rules[Manipulabilité coalitionnelle du vote par note à trois niveaux: Quantification et comparaison à trois autres règles de vote]

All non dictatorial voting rules are susceptible to be manipulated by a group of agents; however, some voting rules are more vulnerable to strategic manipulation than others. The vulnerability of a voting rule to manipulation can be evaluated by the frequency of unstable voting situations where manipulation is possible. We evaluate in this paper the vulnerability of Evaluative Voting (2,1,0) – EV in what follows – to strategic manipulation by coalitions of voters when voter preferences are trichotomous and three candidates are in contention. In order to compare the performance of EV to the ones of plurality rule, antiplurality (or negative plurality) rule and Borda rule, we also compute the theoretical frequency of unstable voting situations for each of these three voting rules when they are extended to the trichotomous framework.