MAJORITY VOTING RULE AND OLIGARCHIC SOCIAL CHOICE RULES

The Institute of Economics and Social Sciences of

Bilkent University

by

PELİN PASİN

In Partial Fulfilment of the Requirements for the Degree of MASTER OF ARTS

in

THE DEPARTMENT OF ECONOMICS BİLKENT UNIVERSITY

ANKARA

October 2001

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I certify that I have read this thesis and have found that it is fully adequate, in scope and in quality, as a thesis for the degree of Master of Arts --------------------------------- Professor Farhad Husseinov Supervisor I certify that I have read this thesis and have found that it is fully adequate, in scope and in quality, as a thesis for the degree of Master of Arts --------------------------------- Assistant Professor Tarık Kara Examining Committee Member I certify that I have read this thesis and have found that it is fully adequate, in scope and in quality, as a thesis for the degree of Master of Arts --------------------------------- Associate Professor Azer Kerimov Examining Committee Member Approval of the Institute of Economics and Social Sciences --------------------------------- Professor Kürşat Aydoğan Director

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ABSTRACT

MAJORITY VOTING RULE AND OLIGARCHIC SOCIAL CHOICE RULES

Pelin Pasin

M.A., Department of Economics

Supervisor: Farhad Husseinov

October 2001

In the first part of this study majority voting rule for two alternatives and

continuum agents is characterized. As in the finite agent case, symmetry among agents,

neutrality between alternatives and positive responsiveness characterize majority voting

rule. In the second part, the relation between T-monotonicity and the group which acts as

the oligarchy in an oligarchic social choice rule, is analyzed. It is shown that the minimal

coalition for which the social choice rule is monotonic constitutes the oligarchy.

Keywords: Social Choice, Majority Voting, Monotonicity, Oligarchy.

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ÖZET

OY ÇOKLUĞU SEÇİM KURALI VE OLİGARŞİK SOSYAL SEÇİM KURALLARI

Pelin Pasin

Yüksek Lisans, İktisat Bölümü

Tez yöneticisi: Farhad Husseinov

Ekim 2001

Bu çalışmanın ilk bölümünde, iki alternatif ve kontinuum temsilci için oy çokluğu

seçim kuralı karakterize edilmiştir. Sonlu temsilci durumunda olduğu gibi, temsilcilerde

simetriklik, alternatifler arasında tarafsızlık ve pozitif cevaplılık oy çokluğu seçim

kuralını karakterize eder. İkinci bölümde, T-monotonluk ve oligarşik bir sosyal seçim

kuralında oligarşi olarak davranacak grup arasındaki ilişki analiz edilmiştir. Sosyal seçim

kuralının monotonluğu sağladığı en küçük grubun oligarşiyi oluşturduğu gösterilmiştir.

Anahtar Kelimeler: Sosyal Seçim, Oy cokluğu, Monotonluk, Oligarşi.

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ACKNOWLEDGMENTS

I am deeply grateful to my supervisor, professor Farhad Husseinov, whose

knowledge and efforts throughout my studies have been a major source of support. I am

also indebted to Assistant Professor Tarık Kara and Associate Professor Azer Kerimov

for accepting to review this material and for their valuable suggestions.

I would like to thank also to my family and my friends, especially Seçil Gergün, for their

support and encouragement.