Contingent valuation is a survey-based economic technique for the valuation of non-market resources, such as environmental preservation or the impact of externalities like pollution. While these resources do give people utility, certain aspects of them do not have a market price as they are not directly sold – for example, people receive benefit from a beautiful view of a mountain, but it would be tough to value using price-based models. Contingent valuation surveys are one technique which is used to measure these aspects. Contingent valuation is often referred to as a stated preference model, in contrast to a price-based revealed preference model. Both models are utility-based. Typically the survey asks how much money people would be willing to pay (or willing to accept) to maintain the existence of (or be compensated for the loss of) an environmental feature, such as biodiversity. History Contingent valuation surveys were first proposed in theory by S.V. Ciriacy-Wantrup (1947) as a method for eliciting market valuation of a non-market good. The first practical application of the technique was in 1963 when Robert K. Davis used surveys to estimate the value hunters and tourists placed on a particular wilderness area. He compared the survey results to an estimation of value based on travel costs and found good correlation with his results. This work was published as his Ph.D. Dissertation at Harvard "The Value of Outdoor Recreation: An Economic Study of the Maine Woods." See also: This work, and other early applications of the method are described in Chapter 1 of "Using Surveys to Value Public Goods" by Robert Cameron Mitchell, and Richard T. Carson The method rose to high prominence in the USA in the 1980s when government agencies were given the power to sue for damage to environmental resources which they were trustees over. Following Ohio v Department of the Interior, the types of damages which they were able to recover included non-use or existence values. Existence values are unable to be assessed through market pricing mechanisms, so contingent valuation surveys were suggested to assess them. During this time, the EPA convened an important conference with an aim to recommend guidelines for survey design. The Exxon Valdez oil spill in Prince William Sound was the first case where contingent valuation surveys were used in a quantitative assessment of damages. Use of the technique has spread from there. Past controversies Many economists question the use of