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Abstract
Two choice modelling studies in Australia were designed to test for the effects of variations
in geographic scale and scope on WTP values. One case study assessed values for improved
natural resource management in a river catchment, and the other assessed values for
improved protection of the Great Barrier Reef. The results show that increases in the amount
of an amenity offered are valued positively and display diminishing marginal utility. Unit
value estimates vary inversely with increases in the geographic scope over which an amenity
improvement was offered. In the case studies, marginal values for the same unit of
environmental improvement could be several thousand times higher when only very small
areas were considered compared to when the whole amenity was framed. These results
confirm that calibration factors are needed in benefit transfer applications between different
geographic scopes. A close inverse relationship was identified between the ratio of quantities
involved and the ratio of the WTP amounts. A log-log form of this relationship is
recommended as a simple and efficient way of performing this calibration.