1. Institute of Environmental Sciences (CML); Leiden University; P.O. Box 9518,2300 RA Leiden The Netherlands
2. Bren School of Environmental Sciences and Management; University of California; Santa Barbara USA
3. Department of Decision Sciences; Management Science Laboratory, SDA Bocconi Business School, Bocconi University; Via Roentgen 1; 20136 Milan Italy
4. Department of Economeasures and Operations Research; VU University Amsterdam; Amsterdam The Netherlands