Overview
1
Costly Information Acquisition: Martinelli (JET, 2006)
2
Jury Deliberation: Geradi and Yariv (JET, 2007), Goeree and Yariv
(Ecma, 2011)
1/22
Costly Information Acquisition
Suppose that it costs time and effort to acquire information.
(e.g. Read

Arrows Theorem
January 29, 2016
1/18
Three or more Alternatives
Can we extend simple majority rule to three or more alternatives and
keep the good properties?
Example:
P1 : x y z
P2 : y z x
P3 : z x y
2/18
Condorcet
Consider a PAR as an extension of simpl

The Model (Information Aggregation)
Lets set up a formal model
Jurors: cfw_1, 2, . . . , N (an odd number)
States of the world: cfw_G , I
Pr (G ) =
Pr (I ) = 1
Information:
Each juror j receives a (conditionally independent) signal sj cfw_g , i.
Pr (g

Voting Rule
Definition 1
A voting rule is a function f : P n X (i.e., f (P1 , . . . , Pn ) X ).
We consider only single-winner voting rules.
(The main results go through to multi-winner voting rules).
The definition covers, e.g., Instant Run-off Voting,
F

Term Paper
Research questions:
Elections are fine.
But remember: preference aggregations are everywhere.
It is often much easier to find a topic from your personal
experiences.
10/26
Term Paper
State some motivation and background for your question.
Why i

What is this course about?
We study systems/institutions for making collective choices, choices that
affect a group of people.
I
Election.
I
Ballot Proposition (e.g., in California): medical marijuana, same-sex
marriage.
I
Board of Directors: selecting, r

A Strategic Voting Model
A simplified version of a strategic voting model in Myerson and Weber
(APSR, 1993)
Voters cfw_1, . . . , N.
Candidates cfw_1, . . . , K .
Payoffs un = (un1 , . . . , unk ).
The set of strategies V
(e.g., with three candidates cfw_

Empirical Analysis: Japanese Election
Kawai and Watanabe (American Economic Review, 2013)
Data: Japanese House of Representatives election held in 2005.
From the data, we back out the voters preferences and the
proportions of strategic voters.
Counterfact

A Special Case: Two Alternatives
We study
Mays Theorem:
Informally: simple majority is the only good voting rule
Good: what are the criteria?
Unique: How to show that a good voting rule is unique?
1/6
Environment (i.e., Economy, Market)
(Notations are fro

Strategic Voting: Overview
We study game theoretic voting models.
- Voters (i.e., game players) are strategic (i.e., rational in game theory
terminology).
(c.f., sincere voters = naive game players.)
Three main topics:
1
Evidences of strategic voting,
2
F

Single Peaked Preferences
X = cfw_y , z. R (i.e., there is some left-right ordering)
N = cfw_1, 2, . . . , n (n is an odd number. No ties.)
For i N, let xi X be the maximal alternative for Pi , and
satisfaction increases as we approach xi (single-peaked).