On Strategies for Candidates in Voting with Partial Information and Open-List Proportional Representation

The Hong Kong University of Science and Technology
Department of Computer Science and Engineering


PhD Thesis Defence


Title: "On Strategies for Candidates in Voting with Partial Information 
and Open-List Proportional Representation"

By

Mr. Ning DING


Abstract

Voting is a popular method to select a political leader or representatives 
in people's social life. Social choice theory studies such preference 
aggregation methods systematically. One of the problems that social choice 
theorists cares the most is voter manipulation. The Gibbard-Satterthwaite 
impossibility theorem states that there is no reasonable social choice 
function that is free from voter manipulation. In an election there are 
not only voters, but also candidates who can think strategically as well. 
In this thesis, we study the strategic behaviors of a candidate in two 
scenarios: voting with partial information, and open-list proportional 
representation.

Traditional social choice theory assumes that voters preferences are 
total orders on the set of candidates. Voting with partial information 
studies what happens before an election when voters' preferences are given 
by partial orders, and the outcomes of the elections may still be open. In 
this case, a candidate may be interested in knowing if it is still 
possible for him to win, and if so, how he can win. To address these 
problems, we consider various forms of queries that candidates can query 
the voters to elicit their preferences and minimal sets of such queries to 
ask in order to determine the outcome of the election with respect to the 
candidate. Our main technical results are that for pair-wise comparison 
queries, there is a unique minimal set and to compute such minimal set is 
in general computationally hard.

Another setting where candidates or political parties need to think 
strategically is in open-list proportional representation. In this thesis 
we consider open-list proportional representation used in Hong Kong 
Legislative Council Geographical Committee election. In this election, 
voters vote on lists of candidates. The strategies of the parties are to 
make up lists of candidates, either on their own or with other parties so 
as to win maximal number of seats. In this thesis we consider the simple 
case when there are just two parties, and model it as a competitive game 
between the two parties, characterize their strategies and analyze the 
equilibrium of this game. Our main results are that this game always has a 
pure strategy Nash equilibrium, but to compute this equilibrium is in 
general intractable.


Date:			Friday, 22 August 2014

Time:			10:00am - 12:00noon

Venue:			Room 3501
 			Lifts 25/26

Chairman:		Prof. Min Zhang (HUMA)

Committee Members:	Prof. Fangzhen Lin (Supervisor)
 			Prof. Mordecai Golin
 			Prof. Ke Yi
 			Prof. Wooyoung Lim (ECON)
 			Prof. Jerome Lang (Universite Paris-Dauphine)


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