Abstract
For many voting rules, it is NPhard to compute a successful manipulation.
However, NPhardness only bounds the worstcase complexity. Recent
theoretical results suggest that manipulation may often be easy in practice. We
study empirically the cost of manipulating the single transferable vote (STV) rule. This was one of the first rules shown to be NPhard to manipulate. It also appears to be one of the harder rules to manipulate since it involves multiple rounds and since, unlike many other rules, it is NPhard for a single agent to manipulate without weights on the votes or uncertainty about how the other agents have voted. In almost every election in our experiments, it was easy to compute how a single agent could manipulate the election or to prove that manipulation by a single agent was impossible. It remains an interesting open question if manipulation by a coalition of agents is hard to compute in practice.
BibTeX  Entry
@InProceedings{walsh:DSP:2010:2558,
author = {Toby Walsh},
title = {Manipulability of Single Transferable Vote},
booktitle = {Computational Foundations of Social Choice},
year = {2010},
editor = {Felix Brandt and Vincent Conitzer and Lane A. Hemaspaandra and JeanFrancois Laslier and William S. Zwicker},
number = {10101},
series = {Dagstuhl Seminar Proceedings},
ISSN = {18624405},
publisher = {Schloss Dagstuhl  LeibnizZentrum fuer Informatik, Germany},
address = {Dagstuhl, Germany},
URL = {http://drops.dagstuhl.de/opus/volltexte/2010/2558},
annote = {Keywords: Computational social choice, manipulability, STV voting, NPhardness}
}
Keywords: 

Computational social choice, manipulability, STV voting, NPhardness 
Seminar: 

10101  Computational Foundations of Social Choice 
Issue Date: 

2010 
Date of publication: 

20.05.2010 