Charge Your Friends for Borrowing Your Stuff Kijung Shin Euiwoong Lee Dhivya Eswaran Ariel Procaccia Carnegie Mellon University Motivation Sharable Goods Used rarely ID: 626064
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Slide1
Why You Should Charge Your Friends for Borrowing Your Stuff
Kijung Shin, Euiwoong Lee, Dhivya Eswaran, Ariel ProcacciaCarnegie Mellon University Slide2
Motivation: Sharable GoodsUsed rarelyGladly lend them to friends, friends of friends, etc.Reluctant to lend them to strangersWhy You Should Charge Your Friends for Borrowing Your Stuff (by Kijung Shin)2/25
Introduction
Analysis
Simulation
Models
ConclusionSlide3
Motivation: Social InefficiencyPeople with many friendsPeople with few friends
Why You Should Charge Your Friends for Borrowing Your Stuff (by Kijung Shin)3/25Efficiencyof PurchaseLikelihoodof Purchase
High
(share with many)
Low
(share with few)
c
an be
Low
(likely to borrow)
c
an be
High
(likely to buy)
Introduction
Analysis
Simulation
Models
ConclusionSlide4
Goal and MethodsGoal: to examine incentives to buy sharable goodsQuestions:How bad can the social inefficiency be?If rent fee can be charged, does it reduce the inefficiency?If so, how much of the inefficiency can be reduced?Approaches:Game-theoretical modelsEquilibrium analysis (PoA and PoS
)SimulationWhy You Should Charge Your Friends for Borrowing Your Stuff (by Kijung Shin)4/25
Introduction
Analysis
Simulation
Models
ConclusionSlide5
Road MapWhy You Should Charge Your Friends for Borrowing Your Stuff (by Kijung Shin)5/25
Introduction
Game-theoretic Models
Sharable Good Game
<<
Sharable
Good
Game with Access Cost
Equilibrium Analysis
Simulation
ConclusionSlide6
TerminologiesSocial networkgraph where nodes are people and edges indicate friendship-hop neighbors of a nodeset of nodes with distance or less from the node
Why You Should Charge Your Friends for Borrowing Your Stuff (by Kijung Shin)6/25
c
c
Introduction
Analysis
Simulation
Models
ConclusionSlide7
Sharable Good Game (SGG)Consider a good sharable with -hop neighborsPlayers: nodes on a social networkActions: buy a good ( ) or not buy ( )Utilities: owner:
(benefit) – (price) ()free rider: (benefit) underprivileged: 0 Why You Should Charge Your Friends for Borrowing Your Stuff (by Kijung Shin)7/25
owner
underprivileged (2-hop neighbor)
f
ree rider (1-hop neighbor)
:
)
Introduction
Analysis
Simulation
Models
ConclusionSlide8
Equilibrium in SGGUtility comparison:free rider > owner > underprivilegedConditions for a Nash Equilibrium (NE)no underprivileged nodesowners have distance at least
Why You Should Charge Your Friends for Borrowing Your Stuff (by Kijung Shin)8/25
not NE
NE
NE
Introduction
Analysis
Simulation
Models
ConclusionSlide9
Social Inefficiency in SGGHighly inefficient NEs happen ifhigh-degree nodes free rideslow-degree nodes has to buy a goodHigh-degree nodes easily lose incentivesas soon as one of its -hop neighbors buy a good
Why You Should Charge Your Friends for Borrowing Your Stuff (by Kijung Shin)9/25
Inefficient NE (5 owners)
Efficient NE(1 owner)
Introduction
Analysis
Simulation
Models
ConclusionSlide10
Road MapWhy You Should Charge Your Friends for Borrowing Your Stuff (by Kijung Shin)10/25
Introduction
Game-theoretic Models
Sharable Good Game
Sharable
Good
Game with Access Cost <<
Equilibrium Analysis
Simulation
ConclusionSlide11
SGG with Access Cost (SGG-AC)Consider a good sharable with -hop neighborsPlayers: nodes in a social networkActions: buy a good ( ) or not buy ( ) rent
a good ( ) by paying an access cost to an owner within -hops Why You Should Charge Your Friends for Borrowing Your Stuff (by Kijung Shin)11/25
)
buy
rent
rent
:
Introduction
Analysis
Simulation
Models
ConclusionSlide12
Utilities in SGG-ACUtilities: owner: (benefit) (price) (access cost)
(# renters)renter: (benefit) (access cost) ()underprivileged: Rich owner and poor ownerrich owner: owner with at least
renters
poor owner
: owner with less than
renterUtility comparison:
rich owner > renter > poor owner > underprivileged
Why You Should Charge Your Friends for Borrowing Your Stuff (by Kijung Shin)
12
/25
Introduction
Analysis
Simulation
Models
ConclusionSlide13
Equilibrium in SGG-ACConditions for Nash Equilibrium (NE)no underprivileged nodespoor owners have no other owners within k-hopsWhy You Should Charge Your Friends for Borrowing Your Stuff (by Kijung Shin)13/25
not NE NE with 2 owners(inefficient NE)NE with 1 owner(efficient NE)
Introduction
Analysis
Simulation
Models
ConclusionSlide14
Social Inefficiency in SGG-ACCan access cost reduce the social inefficiency?It gives high-degree nodes incentives to buy a good even when they can rent a goodif they can be a rich owner Why You Should Charge Your Friends for Borrowing Your Stuff (by Kijung Shin)14/25
most efficient NE in SGG-AC
…
…
…
…
most efficient NE in SGG
Introduction
Analysis
Simulation
Models
ConclusionSlide15
Road MapWhy You Should Charge Your Friends for Borrowing Your Stuff (by Kijung Shin)15/25
Introduction
Game-theoretic Models
Sharable Good Game
Sharable
Good
Game with Access Cost
Equilibrium Analysis
<<
Simulation
ConclusionSlide16
Measuring InefficiencyWe measure social inefficiency simply in terms of the number ownersIn Nash Equilibria and social optima, sum of utilities =
(benefit) (# nodes) (price) (# owners)
Why You Should Charge Your Friends for Borrowing Your Stuff (by Kijung Shin)
16/25
F
ixed
Introduction
Analysis
Simulation
Models
ConclusionSlide17
Measuring Inefficiency (cont.)Given a graph,Given a graph,Why You Should Charge Your Friends for Borrowing Your Stuff (by Kijung Shin)17/25# owners in social optima
# owners in the NESocial inefficiency of an NE := PoA (Price of Anarchy) maximum social inefficiency
over all NEsPoS
(Price of Stability)
:
=
minimum social inefficiency
over
all
NEs
:
=
Introduction
Analysis
Simulation
Models
ConclusionSlide18
Equilibrium AnalysisWhy You Should Charge Your Friends for Borrowing Your Stuff (by Kijung Shin)18/25Worst-case analysis in the worst graph with nodes
High PoA and PoS in SGG without access cost …
…
…
…
…
s
ocial optimum
best NE in SGG
w
orst NE in SGG
…
Introduction
Analysis
Simulation
Models
ConclusionSlide19
Equilibrium Analysis (cont.)Why You Should Charge Your Friends for Borrowing Your Stuff (by Kijung Shin)19/25Increasing
(i.e., sharing goods with more people) reduces PoA and PoSAccess cost in SGG-AC significantly reduces PoS
social optimum= best NE in SGG-AC
…
…Slide20
Road MapWhy You Should Charge Your Friends for Borrowing Your Stuff (by Kijung Shin)20/25
Introduction
Game-theoretic Models
Sharable Good Game
Sharable
Good
Game with Access Cost
Equilibrium Analysis
Simulation <<
Conclusion
Introduction
Analysis
Simulation
Models
ConclusionSlide21
Why Simulation?Complement our theoretical analysisRealistic NEs are obtained by best-response dynamicsReal social networks:Karate club (34 nodes, 78 edges)Hamsterster (1,858 nodes, 12,534 edges)Advogato (5,155 nodes, 51,127 edges)
Why You Should Charge Your Friends for Borrowing Your Stuff (by Kijung Shin)21/25
Introduction
Analysis
Simulation
Models
Conclusion
Theoretical
a
nalysis
Simulation
Equilibria
worst and best NEs
realistic NEs
Graphs
worst graphs
real
social
networksSlide22
Simulation ResultsAverage social inefficiency of 1,000 NEs ()Social inefficiency on real-world networks is about 3.9 with no access costreduced to about 1.8 with a proper access cost
Proper access cost is between 1/3 and 1/2 of price Why You Should Charge Your Friends for Borrowing Your Stuff (by Kijung Shin)22/25
Introduction
Analysis
Simulation
Models
ConclusionSlide23
Simulation Results (cont.)Why You Should Charge Your Friends for Borrowing Your Stuff (by Kijung Shin)23/25
Social inefficiency tends to decrease as increases (i.e., goods are shared with more people)
Introduction
Analysis
Simulation
Models
ConclusionSlide24
Road MapWhy You Should Charge Your Friends for Borrowing Your Stuff (by Kijung Shin)24/25
Introduction
Game-theoretic Models
Sharable Good Game
Sharable
Good
Game with Access Cost
Equilibrium Analysis
Simulation
Conclusion
<<Slide25
ConclusionGoal: examine incentives to buy sharable goodsApproaches:game-theoretic models (SGG & SGG-AC)Equilibrium analysis (PoA and PoS)simulation (best response dynamics)Findings:social inefficiency occurs in Nash equilibria
the inefficiency decreases as goods are shared with more people (i.e., increases)the inefficiency can be significantly reduced by charging free riders an access cost and paying it to owners Why You Should Charge Your Friends for Borrowing Your Stuff (by Kijung Shin)25/25
Introduction
Analysis
Simulation
Models
Conclusion