Abstract Soil nutrient loss due to soil erosion and removal in harvest with traditional farming methods where farmers do not use any fertilisers threatens the sustainability of vegetable productions in the Philippine uplands. Consequently, poor farmers are losing incomes due to declining yields....

In this paper, the results of empirical studies that applied two widely used methods - numerical certainty scale (NCS) and polychotmous choice (PC) - for estimating preference uncertainty adjusted willingness to pay (WTP) in contingent valuation (CV), are summarized. For this review, a number of...