Gillet, J., Schram, A. and Sonnemans, J. (2009). The tragedy of the commons revisited: the Importance of group decision-making Journal of Public Economics, 93(5-6):785--797.
Schram, A. and Onderstal, S. (2009). Bidding to give: an experimental comparison of auctions for charity International Economic Review, 50(2):431--457.