Specific Tastes or Cliques of Jurors? How to Reduce the Level of Manipulation in Group Decisions?

We propose a modification of the standard Borda count which significantly reduces the level of manipulation demonstrated in experiments and observed in actual voting. The method may be applied in voting systems in which the Borda count is usually adopted, e.g. musical competitions, elections in educational institutions and professional and technical societies, sports awards, and even some political elections. We first analyze the actual voting results in the 2016 Henryk Wieniawski International Violin Competition. We show that some jurors are suspected of having exploited a weakness in the standard Borda count method to manipulate the final results. We then consider modifications of the Borda count with a view to designing a method more resistant to manipulation. We show that discarding all the scores of the 20% of jurors who deviate most from the jury average gives a ranking that agrees with public opinion and general expert consensus. Modifications of the Borda count were then experimentally tested against their resistance to manipulability. The results clearly show that excluding jurors has very good statistical properties to recover the objective order of the contestants. Most importantly, however, it dramatically reduces the level of manipulation demonstrated by subjects playing the role of jurors. Finally, we present the mathematical properties of the method proposed. We show that the new method is a compromise between the Majority Criterion and the standard Borda count in that it offers more “consensus-based” rankings than the former while being less vulnerable to manipulation than the latter.