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Exit for Cooperation --A Simulation Study--

This study explores free-riding and mobility in modern societies through an agent-based simulation focusing on the evolution of cooperation and strategies matching. It investigates the effects of mobility on the free-rider problem and the evolution of cooperation when goods have externalities. The simulation involves agent-based modeling in Java, analyzing the impact of mobility cost on cooperation strategies, such as Moving TFT, Fixed TFT, Moving All D, and Fixed All D. The study aims to understand how mobility influences cooperation dynamics and the outcomes of different cooperation strategies in the presence of free riders. Through multiple simulations and game iterations, the study reveals insights on cooperation evolution, the role of defection, and the importance of strategy matching for successful cooperation in diverse settings.

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Exit for Cooperation --A Simulation Study--

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  1. Exit for Cooperation--A Simulation Study-- Yuhsuke Koyama (Tokyo Tech) Hirokuni Ooura (Teikyo) Jun Kobayashi (Chicago) August 15, 2004 ASA, San Francisco

  2. OVERVIEW • Free-riding and Mobility? • Simulation, Agent-Based • EVOLUTION of Cooperation • MATCHING among Strategies

  3. QUESTION • Modern Societies... MOBILITY • Turnover, Divorce, Moving, Immigration • Globalization, Internet • Effects of MOBILITY on FREE-RIDER PROBLEM? • EVOLUTION of Cooperation???

  4. FREE-RIDER PROBLEM • When Goods have Externality • Promise, Donation • Teamwork, Social Movement • RATIONAL to FREE-RIDE • but EFFICIENT to COOPERATE

  5. OUT-FOR-TAT (Hayashi) • Simulation, 2-person game • “EXITING” is Effective as Revenge if Mobility Cost is HIGH • MULTIPLE-PERSON Games? Free-rider Cooperator

  6. Introduction Method Result

  7. SIMULATION • AGENT-BASED, JAVA • SHARE Change of 4 Strategies • MOVING TFT (MT) • FIXED TFT (FT) • MOVING ALL D (MD) • FIXED ALL D (FD) (Move to Most Profitable, Largest) • Cooperators can REJECT??? Cooperator

  8. GAME • 100 Agents • Each with 1 of 4 Strategies • Randomly Assigned to 10 Groups • Free-rider Problem x 5 rounds -> Exit Option • Free-rider Problem x 5 rounds -> Exit Option • (repeated till 20 Exit Options) 100

  9. A B ... J Free-rider Problem Exit Option

  10. FREE-RIDER PROBLEM • Resource $4 • PROVIDE or NOT • Pooled Resources DOUBLED • EQUALLY Distributed in Group • u (Provide) = 8 • u (Not) = 8 + 4 # Providers Group Size # Providers -1 Group Size

  11. EVOLUTION • SHARE CHANGE after Game • Proportional to PAYOFF x SHARE • Mobility Cost = $1 • Repeat 100 Games • 3 Possible OUTCOMES • ALL Cooperators • ALL Defectors • Draw (Otherwise)

  12. WINS and LOSSES • # Strategies = Multiples of 5 • All Initial Distributions = 1,771 • 30 Iterations for Each Distribution • “WIN” if Cooperators Dominate 21 • “LOSS” if 10 Iterations (H0: Even, p<.05, Two-sided Test)

  13. FOCUS • Defectors Reject Cooperators • Many Cooperators+Few Defectors • Initial Distributions -> WINS??? Fixed Defector Moving TFT Fixed TFT Moving Defector

  14. Introduction Method Result

  15. 0 and 5 FIXED DEFECTORS Fixed Defector MT FT Moving Defector WIN LOSS

  16. 10, 15, 20 FIXED DEFECTORS FT 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 0 30 30 28 30 29 30 28 29 30 28 29 25 28 22 27 26 18 10 1 22 21 16 11 16 16 11 8 14 11 6 11 12 11 12 8 8 2 14 9 10 6 13 11 6 7 4 3 6 5 3 7 3 4 5 MD 3 7 7 8 6 6 3 5 4 4 1 2 3 5 1 3 2 4 4 2 4 4 1 4 1 2 2 1 0 2 3 2 4 2 5 2 5 4 0 1 4 2 1 1 1 0 3 0 7 3 1 1 3 0 MD 0 24 25 24 21 24 27 23 20 24 26 25 19 15 15 10 10 4 Fixed Defector MT FT Moving Defector

  17. 1. EVOLUTION of COOPERAITON • Cooperators can REJECT (Blue) • If FEW Defectors • Even with MOBILITY • Up to about 15 Defectors • b/c 10 Groups

  18. 2. MATCHING • Cooperators Refuse TOGETHER Fixed Defector Moving TFT Fixed TFT Moving Defector

  19. SUMMARY • 1. Evolution of Cooperation Even with Mobility • 2. MATCHING matters • More STRATEGIES? • More MOBILITY COSTS? • Compare with Experiment, Survey

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