Costly Information Acquisition: Martinelli (JET, 2006)
Jury Deliberation: Geradi and Yariv (JET, 2007), Goeree and Yariv
Costly Information Acquisition
Suppose that it costs time and effort to acquire information.
January 29, 2016
Three or more Alternatives
Can we extend simple majority rule to three or more alternatives and
keep the good properties?
P1 : x y z
P2 : y z x
P3 : z x y
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
Each juror j receives a (conditionally independent) signal sj cfw_g , i.
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,
Elections are fine.
But remember: preference aggregations are everywhere.
It is often much easier to find a topic from your personal
State some motivation and background for your question.
What is this course about?
We study systems/institutions for making collective choices, choices that
affect a group of people.
Ballot Proposition (e.g., in California): medical marijuana, same-sex
Board of Directors: selecting, r
A Strategic Voting Model
A simplified version of a strategic voting model in Myerson and Weber
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.
A Special Case: Two Alternatives
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?
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
(c.f., sincere voters = naive game players.)
Three main topics:
Evidences of strategic voting,
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).