Unlike other contingent valuation methods that use bidding approaches, especially double bounddichotomous choices, this method allowed us to avoid the problem of bias resulting from changes inthe incentive structure [28–30]. The interval data model includes more information and can improvethe eciency of estimation [31]. For this study, we denote an observable variable WTP. If Respondent i indicates that his willingness to pay is very weak, then WTPi = 1; similarly, if the WTP is weak, then WTPi = 2; if moderate, WTPi = 3; if strong, WTPi = 4; and if very strong, WTPi = 5. The corresponding probability for WTPi = j1 is expressed as the following equation: