1. Eileen O. van Ravenswaay: Emerging Demands on our Food and Agricultural System: Developments in Environmental Labelling. Staff Paper No. 96-88, Department of Agricultural Economics, Michigan State University, 1996.
2. S. Leubuscher, W. Hager, C. Wattiez, Jennifer F. Mombrù, E. Liaska: Study on verification and control of environmental product claims, Final Report by Prospect C&S for DG Health and Consumer Protection, 1998. For a study dealing with social labels see S. Zadek, S. Lingayah, M. Forstater: Les labels sociaux: des outils au service du commerce éthique, New economic Foundation, 1998.
3. P. Nelson: Information and Consumer Behavior, in: Journal of Political Economy, Vol. 78, 1970, pp. 311–329; Michael R. Darby, E. Karni: Free Competition and the Optimal Amount of Fraud, in: Journal of Law and Economics, Vol. 16, 1973, pp. 67–88.
4. Gary T. Ford, Darlene B. Smith, John L. Swasy: An Empirical Test of the Search, Experience and Credence Attributes Framework, in: Advances in Consumer Research, Vol. 15, 1988, pp. 239–248; Manfred F. Maute, William R. Forrester: The Effect of Attribute Qualities on Consumer Decision Making: a causal model of external information search. in: Journal of Economic Psychology, vol. 12, 1991, pp. 643–666; Esben S. Andersen, K. Philipsen: The Evolution of Credence Goods in Customer Markets: Exchanging “Pigs in Pokes”, Paper presented at the DRUID Winter Seminar, Middelfart, 8–10, January, 1998.
5. Clement G. Krouse: Theory of Industrial economics, Cambridge Mass. and Oxford, 1992, Blackwell.