Johannes Diederich Heidelberg University   Alfred-Weber-Institute Heidelberg University Bergheimer Str. 20 Heidelberg, 69115 Germany   diederich@eco.uni-heidelberg.de   http://www.eco.uni-heidelberg.de/lehrstuhl/diederich_e.html           JEL Areas: Q5 : Environmental Economics: General C9 : Design of Experiments: General