Voting Procedures for Electing a Single Candidate: Proving Their (In)Vulnerability to Various Voting Paradoxes

147 Pages·2018·1.77 MB·English

by  Dan S. Felsenthal

SPRINGER BRIEFS IN ECONOMICS
Dan S. Felsenthal
Hannu Nurmi
Voting Procedures
for Electing a Single
Candidate
Proving Their
(In)Vulnerability
to Various Voting
Paradoxes
SpringerBriefs in Economics
More information about this series at http://www.springer.com/series/8876
Dan S. Felsenthal Hannu Nurmi
(cid:129)
Voting Procedures
for Electing a Single
Candidate
Proving Their (In)Vulnerability to Various
Voting Paradoxes
123
Dan S.Felsenthal Hannu Nurmi
Schoolof Political Sciences Department ofPolitical Science
University of Haifa University of Turku
Haifa Turku
Israel Finland
ISSN 2191-5504 ISSN 2191-5512 (electronic)
SpringerBriefs inEconomics
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Preface
Free and fair elections are an essential ingredient of democratic governance.
Elections without these attributes can be and have been held, but their connection
with‘thegovernmentofthepeople,bythepeopleandforthepeople’,asAbraham
Lincoln succinctly put it, is tenuous at best. This book focuses on the fairness part
oftheelections.Morespecifically,weaimtoevaluatevotingprocedures—thosein
everyday use and those invented but not yet employed—from thepoint of view of
howfaithfullytheyreflecttheopinionsofthevoters.Itturnsoutthatteasingoutthe
will of the people from the opinions expressed in voting ballots is not at all
straightforward. On the contrary, several mutually exclusive intuitions about what
constitutes being the collectively best candidate, or collectively most desirable
policyalternative, canbefoundinthescholarlyliteratureandinpoliticalparlance.
Indeed, the social choice theory is known for its results establishing incompati-
bilities of various desiderata that one could expect the choice rules—and voting
procedures among them—to satisfy.
This book is a summary of some of the work that has been done on voting
proceduresoverthepastdecadesbynumerousauthorsincludingus.Itscoretextis
the first-named author’s extensive article (Felsenthal 2012), and this book is an
updated and extended version of that text. Many findings reported here are, how-
ever,basedonourearlierworkinthisarea(e.g.Felsenthal&Tideman2013,2014;
Felsenthal & Nurmi 2016, 2017; Nurmi 1983, 1987, 1999, 2012) and some are
published here for the first time.
Although the list of properties or desiderata of voting procedures that we deal
withisratherlong,itisbynomeansexhaustive.Wehavefocusedonpropertiesthat
haveacquiredmostattentioninthescholarlydebates.Weareparticularlyinterested
in various articulations of the notion of winning of elections and in examining the
very rationale of voting. This book can be considered as a companion text of our
Monotonicity Failures Afflicting Procedures for Electing a Single Candidate
(Felsenthal & Nurmi 2017) where the properties related to the rationale of partic-
ipation are in the primary focus. That book along with the present one gives—we
hope—a reasonably broad basis for evaluating voting procedures and—when
augmented with situational parameters—making enlightened choices among them.
v
vi Preface
However, the study of the main paradoxes afflicting various voting procedures
cannotbecompletebeforethenecessaryand/orsufficientconditionsunderwhicha
given paradoxcanoccur under agiven votingprocedureareknown.Asmostsuch
conditions are still unknown, the relative desirability of the various voting proce-
dures must continue to be assessed without robust knowledge regarding the
probability of their occurrence.
Nevertheless, in assessing the relative desirability of various voting procedures,
wehopethatthisbookwillbeusefulnotonlytosocialchoicetheoristsandstudents
but also to students and researchers in related areas concerned with aspects of
decision-making by vote: political science, mathematics, economics, business
administration and constitutional law. It can also be used as a textbook in social
choice courses and, therefore, we included several exercises (and answers to these
exercises) at the end of each chapter of this book.
In the course of decades when studying voting procedures individually and
jointly,we haveincurrednumerous intellectualdebts,indeed,toonumerousfor all
ofthemtobeexplicitlymentionedhere.Sowejustwanttoextendourthankstoour
former co-authors inthis field: PaulR. Abramson, Fuad Aleskerov, Adiel Teixeira
de Almeida, Sven Berg, Steven J. Brams, Avraham Brichta, Vincent Chua,
Abraham Diskin, Mario Fedrizzi, Manfred J. Holler, Janusz Kacprzyk, Moshé
Machover, Ze’ev Maoz, Tommi Meskanen, Nicholas Miller, Per Molander, Lasse
Nurmi, Amnon Rapoport, Donald G. Saari, Nicolaus Tideman and Slawomir
Zadrozny.
We are also grateful to Dr. Martina Bihn—the Editorial Director Business/
Economics&StatisticsatSpringer—forherexcellentandsmoothcooperation;and
to Judith Kripp and Kay Stoll of Springer’s staff, as well as to Sooryadeepth
JayakrishnanofScientificPublishingServicesLtd.,India,whomadethepublication
of this bookin its presentform possible.
Jerusalem, Israel Dan S. Felsenthal
Turku, Finland Hannu Nurmi
References
Felsenthal, D.S.(2012).Reviewofparadoxesafflictingproceduresforelectingasinglecandidate.
InD.S.Felsenthal&M.Machover(Eds.),Electoralsystems:Paradoxes,assumptions,and
procedures(pp.19–92).Berlin,Heidelberg:Springer,Chap.3.
Felsenthal, D. S., & Nurmi, H. (2016). Two types of participation failure under nine voting
methodsinvariableelectorates.PublicChoice,168,115–135.
Felsenthal, D.S.,&Nurmi,H.(2017).Monotonicityfailuresafflictingproceduresforelectinga
singlecandidate.Cham,Switzerland:Springer.
Felsenthal, D. S., & Tideman, N. (2013). Varieties offailure of monotonicity and participation
underfivevotingmethods.TheoryandDecision,75,59–77.
Felsenthal, D.S.&Tideman,N.(2014).Interactingdoublemonotonicityfailurewithdirectionof
impactunderfivevotingmethods.MathematicalSocialSciences,67,57–66.
Preface vii
Nurmi, H.(1983).Votingprocedures:Asummaryanalysis.BritishJournalofPoliticalScience,
13,181–208.
Nurmi, H.(1987).Comparingvotingsystems.Dordrect:D.Reidel.
Nurmi, H.(1999).Votingparadoxesandhowtodealwiththem.Berlin,Heidelberg,NewYork:
Springer
Nurmi, H. (2012). On the relevance of theoretical results to voting system choice. In D.
S. Felsenthal & M. Machover (Eds.), Electoral systems: paradoxes, assumptions, and pro-
cedures(pp.255–274).Berlin,Heidelberg:Springer,Chap.10.
Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Answers to Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2 Voting Paradoxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.1 Simple Paradoxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.1.1 The Condorcet Winner Paradox . . . . . . . . . . . . . . . . . . 8
2.1.2 The Absolute Majority Winner Paradox. . . . . . . . . . . . . 8
2.1.3 The Condorcet Loser or Borda Paradox. . . . . . . . . . . . . 8
2.1.4 The Absolute Majority Loser Paradox. . . . . . . . . . . . . . 9
2.1.5 The Pareto (or Dominated Candidate) Paradox. . . . . . . . 9
2.2 Conditional Paradoxes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2.1 Additional Support (or Lack of Monotonicity or
Negative Responsiveness) Paradox . . . . . . . . . . . . . . . . 9
2.2.2 Reinforcement (or Inconsistency or Multiple Districts)
Paradox. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.2.3 Truncation Paradox . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.2.4 No-Show Paradox . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.2.5 Twin Paradox . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.2.6 Violation of the Subset Choice Condition (SCC) . . . . . . 10
2.2.7 Preference Inversion Paradox . . . . . . . . . . . . . . . . . . . . 11
2.2.8 Dependence on Order of Voting (DOV) Paradox . . . . . . 11
Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Answers to Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3 Voting Procedures Designed to Elect a Single Candidate . . . . . . . . . 15
3.1 Non–Ranked Voting Procedures . . . . . . . . . . . . . . . . . . . . . . . . 15
3.1.1 Plurality Voting (aka First Past the Post) Procedure . . . . 15
3.1.2 Plurality with Runoff Voting Procedure. . . . . . . . . . . . . 16
ix
x Contents
3.1.3 Approval Voting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.1.4 Successive Elimination. . . . . . . . . . . . . . . . . . . . . . . . . 16
3.2 Ranked Voting Procedures that are not Condorcet–Consistent . . . 17
3.2.1 Borda’s Count . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
3.2.2 Alternative Vote (aka Instant Runoff) . . . . . . . . . . . . . . 17
3.2.3 Coombs’ Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.2.4 Bucklin’s Method. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.2.5 Range Voting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.2.6 Majority Judgment. . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.3 Ranked Voting Procedures that are Condorcet–Consistent. . . . . . 20
3.3.1 The Minimax Procedure . . . . . . . . . . . . . . . . . . . . . . . . 20
3.3.2 Dodgson’s Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.3.3 Nanson’s Method. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.3.4 Copeland’s Method . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.3.5 Black’s Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.3.6 Kemeny’s Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.3.7 Schwartz’s Method. . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
3.3.8 Young’s Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Answers to Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
4 The (In)Vulnerability of Non-Ranked Voting Procedures
to Various Paradoxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
4.1 The (In)Vulnerability of the Plurality Voting Procedure to
Various Paradoxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
4.1.1 The Condorcet Winner, the Condorcet Loser,
the Absolute Majority Loser, the Preference Inversion,
and the SCC Paradoxes . . . . . . . . . . . . . . . . . . . . . . . . 27
4.1.2 Absolute Majority Winner Paradox . . . . . . . . . . . . . . . . 28
4.1.3 Pareto-Dominated Candidate Paradox . . . . . . . . . . . . . . 28
4.1.4 Lack of Monotonicity Paradox . . . . . . . . . . . . . . . . . . . 28
4.1.5 Reinforcement Paradox. . . . . . . . . . . . . . . . . . . . . . . . . 29
4.1.6 No-Show Paradox . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4.1.7 Truncation Paradox . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4.1.8 Twin Paradox . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4.2 The (In)Vulnerability of the Plurality with Runoff Procedure
to Various Paradoxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
4.2.1 The Condorcet Winner, Lack of Monotonicity,
and the SCC Paradoxes . . . . . . . . . . . . . . . . . . . . . . . . 30
4.2.2 Absolute Majority Winner Paradox . . . . . . . . . . . . . . . . 30
4.2.3 Condorcet Loser and Absolute Majority Paradoxes . . . . 31
4.2.4 Pareto-Dominated Candidate Paradox . . . . . . . . . . . . . . 31
4.2.5 Truncation Paradox . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
4.2.6 Reinforcement Paradox. . . . . . . . . . . . . . . . . . . . . . . . . 32