Economics 113
Prof. R. Starr, Mr. Troy Kravitz
UCSD
Winter 2010
March 9, 2010
1
Lecture Notes, March 9, 2010
Salvaging Majority Rule:
Single Peaked Preferences and the Median
Voter Theorem
Arrow Possibility Theorem implies that majority rule or any similar
decisionmaking mechanism on pairwise alternatives cannot generally lead
to transitive group preferences.
Restriction on space of possible preferences  purposely violate
'Unrestricted Domain';
limit the space of possible profiles.
Single peaked
preferences:
Suppose all propositions to be decided can be linearly ordered,
left to right.
All voters agree on the left to right ordering.
They disagree on
their choices.
Everyone has his favorite point; but
chacun a son gout
 the favorite point
differs among voters.
For each voter, as we move to the left of his favorite
his utility goes down; as we move to the right of his favorite his utility goes
down.
Let L be the "is to the left of" ordering.
All voters agree on the L ordering.
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 Fall '08
 Starr,R
 Economics, Utility, Voting system, Prof. R. Starr

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