Contingent Choice Method (CCM)
CCM asks the respondent to state a preference between one group of environmental services or characteristics, at a given price or cost to the individual, and another group of environmental characteristics at a different price or cost. 

Focuses on tradeoffs among scenarios with different characteristics, contingent choice is especially suited to policy decisions where a set of possible actions might result in different impacts on natural resources or environmental services. 
Useful in valuation of improvements to ecosystems, given that several service flows are often simultaneously affected. 

May also be used to simply rank options, without focusing on dollar values.

Formats for applying contingent choice methods:
Contingent RankingContingent ranking surveys ask individuals to compare and rank alternate program outcomes with various characteristics, including costs.
Discrete ChoiceIn the discrete choice approach, respondents are simultaneously shown two or more different alternatives and their characteristics, and asked to identify the most preferred alternative in the choice. 
Paired Ratingvariation on the discrete choice format, where respondents are asked to
                  compare 2 alternate situations and are asked to rate them in terms of strength of preference.
 
Choices that respondents make are statistically analyzed using discrete choice statistical techniques, to determine the relative values for the different characteristics or attributes.  If one of the characteristics is a monetary price, then it is possible to compute the respondentÕs willingness to pay for the other characteristics.