Bargaining Whoever offers to another a bargain of any kind, proposes to do this. Give me that which...
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Transcript of Bargaining Whoever offers to another a bargain of any kind, proposes to do this. Give me that which...
Bargaining
Whoever offers to another a bargain of any kind, proposes to do this. Give me that which I want, and you shall have this which you want …; and it is this manner that we obtain from one another the far greater part of those good offices we stand in need of. It is not from the benevolence of the butcher, the brewer, or the baker that we expect our dinner, but from their regard to their own interest.
-- A. Smith, 1776
Bargaining
• We Play a Game• Bargaining Games• Credibility• Subgame Perfection• Alternating Offers and Shrinking Pies
We Play a Game
PROPOSER RESPONDER
Player # ____ Player # ____
Offer $ _____ Accept Reject
The Ultimatum Game
OFFERS
5
4
3
2
1
0
REJECTEDACCEPTED
N = 20Mean = $1.30
9 Offers > 0 Rejected1 Offer < 1.00 (20%) Accepted
(3/6/00)
The Ultimatum Game
OFFERS
5
4
3
2
1
0
REJECTEDACCEPTED
N = 32Mean = $1.75
10 Offers > 0 Rejected1 Offer < $1 (20%) Accepted
(2/28/01)
The Ultimatum Game
OFFERS
5
4
3
2
1
0
REJECTEDACCEPTED
N = 38Mean = $1.69
10 Offers > 0 Rejected*3 Offers < $1 (20%) Accepted
(2/27/02)* 1 subject offered 0
The Ultimatum Game
OFFERS
5
4
3
2
1
0
REJECTEDACCEPTED
N = 12Mean = $2.77
2 Offers > 0 Rejected0 Offers < 1.00 (20%) Accepted
(7/10/03)
The Ultimatum Game
0 3.31 5 P1
P2
5
1.69
0
N = 38Mean = $1.69
10 Offers > 0 Rejected*3 Offers < $1 (20%) Accepted
(2/27/02)* 1 subject offered 0
2.50
1.00
What is the lowest acceptable offer?
The Ultimatum Game
Theory predicts very low offers will be made and accepted.
Experiments show:• Mean offers are 30-40% of the total• Mode = 50%• Offers <20% are rare and usually rejected
Guth Schmittberger, and Schwarze (1982)
Kahnemann, Knetsch, and Thaler (1986)
Also, Camerer and Thaler (1995)
The Ultimatum Game
How can we explain the divergence between predicted and observed results?
• Stakes are too low• Fairness
– Relative shares matter– Endowments matter– Culture, norms, or “manners”
• People make mistakes• Time/Impatience
Bargaining Games
Bargaining involves (at least) 2 players who face the the opportunity of a profitable joint venture, provided they can agree in advance on a division between them.
Bargaining involves a combination of common as well as conflicting interests.
The central issue in all bargaining games is credibility: the strategic use of threats, bluffs, and promises.
Bargaining Games
P2
1
0 1 P1
Disagreement
point
Two players have the opportunity to share $1, if they can agree on a division beforehand.
Each writes down a number. If they add to $1, each gets her number; if not; they each get 0.
Every division s.t. x + (1-x) = 1 is a NE.
Divide a Dollar
P1= x; P2 = 1-x.
(0,0) (3,1)
1
2
Chain Store Game
(2,2)
A firm (Player 1) is considering whether to enter the market of a monopolist (Player 2). The monopolist can choose to fight the entrant, or not.
Enter Don’t Enter
Fight Don’t Fight
Credibility
Fight Opera
F O F O
(2,1) (0,0) (0,0) (1,2)
Player 1
Player 2
2, 1 0, 0
0, 0 1, 2
F O
F
O
Is there a credible threat?
Battle of the Sexes
Credibility
FIGHT OPERA
2, 1 0, 0
0, 0 1, 2
FIGHT
OPERA
q
NE = {(1, 1); (0, 0); (2/3, 1/3)} Prudent: {1/3, 2/3)}
p = 2/3
p = 1/3
Battle of the Sexes
Credibility
EP1
2/3
1/3
4/3
FIGHT OPERA
2, 1 0, 0
0, 0 1, 2
FIGHT
OPERA
P1
P2
Credibility
NE = {(1, 1); (0, 0); (2/3, 1/3)}
BATNA
Battle of the Sexes
Best Alternative to a Negotiated Agreement
Subgame: a part (or subset) of an extensive game, starting at a singleton node (not the initial node) and continuing to payoffs.
Subgame Perfect Nash Equilibrium (SPNE): a NE achieved by strategies that also constitute NE in each subgame.
eliminates NE in which the players threats are not credible.
selects the outcome that would be arrived at via backwards induction.
Subgame Perfection
(0,0) (3,1)
1
2
Subgame Perfection
(2,2)
Chain Store Game A firm (Player 1) is considering whether to enter the market of a monopolist (Player 2). Player 2 can then choose to fight the entrant, or not.
Enter Don’t Enter
Fight Don’t Fight
Subgame
(0,0) (3,1)
1
2
Subgame Perfection
(2,2)
Chain Store Game
Enter Don’t
Fight Don’t
0, 0 3, 1
2, 2 2, 2
Fight Don’t
Enter
Don’t
NE = {(E,D), (D,F)}. SPNE = {(E,D)}.Subgame Perfect Nash Equilibrium
A(ccept)
2
H(igh)
1
L(ow)
R(eject)
5,5
0,0
8,2
0,0
Proposer (Player 1) can make
High Offer (50-50%) or Low Offer (80-20%).
Subgame PerfectionMini-Ultimatum Game
A(ccept)
2
H(igh)
1
L(ow)
R(eject)
H 5,5 0,0 5,5 0,0
L 8,2 0,0 0,0 8,2
AA RR AR RA
5,5
0,0
8,2
0,0
Subgame Perfect Nash Equilibrium
SPNE = {(L,AA)}(H,AR) and (L,RA) involve incredible threats.
Subgame PerfectionMini-Ultimatum Game
Subgame Perfection
2
H
1
L
2
H 5,5 0,0 5,5 0,0
L 8,2 1,9 1,9 8,2
5,5
0,0
8,2
1,9
AA RR AR RA
Subgame Perfection
2
H
1
L
H 5,5 0,0 5,5 0,0
L 8,2 1,9 1,9 8,2
5,5
0,0
1,9 SPNE = {(H,AR)}
AA RR AR RA
Alternating Offer Bargaining Game
Two players are to divide a sum of money (S) is a finite number (N) of alternating offers. Player 1 (‘Buyer’) goes first; Player 2 (‘Seller’) can either accept or counter offer, and so on. The game continues until an offer is accepted or N is reached. If no offer is accepted, the players each get zero.
A. Rubinstein, 1982
Alternating Offer Bargaining Game
1
(a,S-a) 2
(b,S-b) 1
(c,S-c) (0,0)
S = $5.00N = 3
Alternating Offer Bargaining Game
1
(a,S-a) 2
(b,S-b) 1
(4.99, 0.01) (0,0)
S = $5.00N = 3
Alternating Offer Bargaining Game 1
(4.99,0.01) 2
(b,S-b) 1
(4.99,0.01) (0,0)
S = $5.00N = 3
SPNE = (4.99,0.01) The game reduces to an Ultimatum Game
Now consider what happens if the sum to be divided decreases with each round of the game (e.g., transaction costs, risk aversion, impatience).
Let S = Sum of money to be divided
N = Number of rounds
= Discount parameter
Shrinking Pie Game
Shrinking Pie Game
S = $5.00N = 3 = 0.5
1
(3.74,1.26) 2
(1.25, 1.25) 1
(1.24,0.01) (0,0)
1
Shrinking Pie Game
S = $5.00N = 4 = 0.5
1
(3.13,1.87) 2
(0.64,1.86) 1
(0.63,0.62) 2
(0.01, 0.61) (0,0)
1
Shrinking Pie Game
0 3.33 5 P1
P2
5
1.67
0
N = 1 (4.99, 0.01) 2 (2.50, 2.50) 3 (3.74, 1.26) 4 (3.13, 1.87)5 (3.43, 1.57)… …This series converges to (S/(1+), S – S/(1+)) =
(3.33, 1.67)
This pair {S/(1+ ),S-S/(1+ )} are the payoffs of the unique SPNE.
for = ½
1
2
3
4
5
Shrinking Pie Game
Optimal Offer (O*) expressed as a share of the total sum to be divided = [S-S/(1+)]/S
O* = /(1+
SPNE = {1- /(1+ ), /(1+ )}
Thus both =1 and =0 are special cases of Rubinstein’s model:
When =1 (no bargaining costs), O* = 1/2
When =0, game collapses to the ultimatum version and O* = 0 (+)
Shrinking Pie GameRubinstein’s solution: If a bargaining game is played in a seriesof alternating offers, and if a speedy resolution is preferred toone that takes longer, then there is only one offer that a rationalplayer should make, and the only rational thing for the opponentto do is accept it immediately! (See Gibbons: 68-71)
Recall that NE is not a very precise solution, because mostgames have multiple NE. Incorporating time imposes aconstraint (bargaining cost) -> selects SPNE from the set of NE.
Even if the final period is unknown (and hence backwardinduction is not possible), it is possible to arrive at a uniqueoutcome that should be (chosen by/agreeable to) rationalplayers.
Bargaining Games
Bargaining games are fundamental to understanding the price determination mechanism in “small” markets.
The central issue in all bargaining games is credibility: the strategic use of threats, bluffs, and promises.
When information is asymmetric, profitable exchanges may be “left on the table.”
In such cases, there is an incentive to make oneself credible (e.g., appraisals; audits; “reputable” agents; brand names; lemons laws; “corporate governance”).
Bargaining & Negotiation
• In real-world negotiations, players often have incomplete, asymmetric, or private information, e.g., only the seller of a used car knows its true quality and hence its true value.
• Making agreements is made all the more difficult “when trust and good faith are lacking and there is no legal recourse for breach of contract” (Schelling, 1960: 20).
• Rubinstein’s solution: If a bargaining game is played in a series of alternating offers, and if a speedy resolution is preferred to one that takes longer, then there is only one offer that a rational player should make, and the only rational thing for the opponent to do is accept it immediately!