Frugal Bribery in Voting
?
†
?
Palash Dey , Neeldhara Misra , and Y. Narahari
?{palash|hari}@csa.iisc.ernet.in † [email protected]
?Indian Institute of Science, Bangalore, India † Indian Institute of Technology, Gandhinagar, India
Unweighted
Weighted
Voting Rule
Frugal-bribery Frugal-$bribery Frugal-bribery Frugal-$bribery
Plurality
P
P
P
NP-complete
Veto
P
P
NP-complete
NP-complete
NP − complete
NP − complete
NP-complete
P
NP − complete•
NP − complete
NP-complete
Borda
NP-complete
NP − complete†
NP-complete
NP-complete
Plurality with runoff
P
?
NP-complete
NP-complete
Maximin
?
NP-complete
NP-complete
NP-complete
Copeland
?
NP-complete
NP-complete
NP-complete
STV
?
NP-complete
NP-complete
NP-complete
Figure 1: Application of voting in AI
k-approval
P
Voting in AI
k-veto
• Recommender
systems, search engine aggregation, multiagent planning, Clarke tax etc.
• However, voting is susceptible to manipulation, bribery, control etc.
?
?- The result holds for k ≥ 5. •- The result holds for k ≥ 3. †- The result holds for a much wider class
of scoring rules. - The results do not hold for the plurality voting rule. ?- The problem is open.
Table 1:
Figure 2: Strategic Manipulation and Bribery
Significance of Results
• Proposed
Problem Overview
• Bribery
in elections is an important problem in computational social choice theory. We
introduce and study two important special cases of the bribery problem, namely,
F RUGAL - BRIBERY and F RUGAL -$ BRIBERY where the briber is frugal in nature. By this, we mean
that the briber is only able to influence voters who benefit from the suggestion of the briber.
formally, a voter is vulnerable if the outcome of the election improves according to her
own preference when she accepts the suggestion of the briber.
two natural models of bribery in voting.
• Our hardness result subsumes the hardness results for shift bribery from the literature [FHH06].
• Thus bribery, although a possible attack on elections in principle, maybe practically not viable.
References
• More
• In
the F RUGAL - BRIBERY problem, the goal is to make a certain candidate win the election by
changing only the vulnerable votes.
• In
the F RUGAL -$ BRIBERY problem, the vulnerable votes have prices and the goal is to make a
certain candidate win the election by changing only the vulnerable votes, subject to a budget
constraint.
[FHH06] Piotr Faliszewski, Edith Hemaspaandra, and
Lane A Hemaspaandra.
The complexity of bribery in elections.
In International Conference on Artificial
Intelligence (AAAI), volume 6, pages 641–646,
2006.
Acknowledgements
Palash Dey wishes to gratefully acknowledge support
from Google India for providing him with a special fellowship for carrying out his doctoral work. Neeldhara Misra acknowledges support by the INSPIRE Faculty
Scheme, DST India (project IFA12-ENG-31).