1. Communication and Cooperation in Social Dilemmas Susanne Abele, Garold Stasser & Christopher Chartier Miami University

2. Communication and Cooperation in Public Good Games Public good provision – Public radio, public transportation – Collective and personal interests at odds How can cooperation be increased? – Communication Kerr & Kaufmann-Gilliland (1994) Kerr et al. (1997)

3. Communication and Cooperation in Public Good Games Examples where communication did not help – Chen & Komorita (1994) Signals need to be binding – Wilson & Snell (1997) Nonbinding signals decreased cooperation How do we rectify these seemingly contradictory results?

4. Communication and Cooperation in Public Good Games Many differences between studies – Nature of communication – Specifics of endowments and payoffs – Type of public good game Kerr & Kaufmann Gilliland (1994), Kerr et al. (1997) – Step-level (minimal contributing set game) Chen & Komorita (1994), Wilson & Snell (1997) – Continuous public good game

5. Continuous Public Good Games Players receive endowment – Allocate to public account or private account Contributions to public account earn interest Players are always better off keeping a unit in their private account instead of contributing Nash equilibrium = all players contribute nothing

6. Step-Level Public Good Games Players receive endowment – Allocate to public account or private account Provision point – Public good provided if met or exceeded – If not met, contributions are lost Players are not always better off withholding contributions

7. Step-Level Public Good Games 4 players with 10 unit endowments 40 unit bonus if 20 units are contributed 3 players contribute 19 total units – If player 4 contributes 1 unit, they earn 19 units – If player 4 contributes nothing, they earn 10 units Many Nash equilibria – All players contribute nothing – Contributions exactly meet the provision point

8. Minimal Contributing Set Games Type of step-level game Players have a dichotomous decision – Contribute full endowment or nothing Provision point specifies how many players must contribute

9. Important Difference between Continuous and Step-Level Games Step-level games (including MCS games) provide the opportunity for coordinated solutions Continuous games do not This difference can lead to differential effects of communication on cooperation

10. Experimental Design 2 (Type of Game: Continuous Public Good Game versus Minimal Contributing Set Game) X 2 (Communication: tentative decision communicated versus no communication)

11. Procedure Groups of 4 with 10 unit endowments Continuous game – Public account earned 100% interest (doubled) MCS game – Provision point of 20 units, earned a 60 unit bonus Communication – Message of tentative decision before trial – All players received all messages before deciding 12 trials

12. Giving by Trial Block Game:ContinuousMin Set Control Cheap Mean Giving per Trial ControlCheap

13. Block 3 Giving Game:ContinuousMin Set Mean giving per Trial

14. Giving and Pledges by Trial Block Game:ContinuousMin Set Pledge Give Mean Giving/Pledge per Trial PledgeGive

15. Giving and Pledges MCS game – Pledged an excess of contributions on an average of 5 trials – When pledges exceeded provision point, the mean difference between pledges and contributions was 4.5 – When they did not, it was 1.1 Continuous game – Control groups earned more than pledging groups

16. Perception of Games Players in a Minimal Contributing Set Game saw each other as more cooperative than did players in a Continuous Public Goods Game by endorsing statements like: ‘My group tried to earn as much as possible for all of us.’ ‘My group tried to keep the differences in our earnings as small as possible.’ ‘The members of my group tried to help each other.’

17. Conclusions Non-binding pledges hurt cooperation in continuous game – Pledge high, contribute low Opportunity for coordinated solution (MCS game) reduced this negative effect Step-level and continuous public good games are not perfectly interchangeable – Differential effects of intervention – Perceived differently by players

18. Thank you