Testing the Internal Consistency of Contingent Valuation Surveys

For an internal consistency check, one can examine WTP responses to different surveys. Holding an environmental problem constant, concave preferences imply WTPconcavein the success of a remedy. The same preferences imply WTPconvexin the magnitude of an environmental problem, assuming a successful remedy. Having opposite signed curvature of these two WTP patterns is general, not requiring concave preferences. For an adding-up test, an environmental commodity can be divided. Then, WTP for one part plus WTP for the second part, conditional on already having the first part, equals WTP for the whole, adjusted by an income effect.