The effects of spatial framing and attribute range on the measurement of nonuse values of biodiversity improvements

Assessing the value of changes in environmental conditions using stated preference valuation studies requires accurate quantification and communication of outcomes that affect human welfare. Using a stated choice experiment to estimate primarily nonuse value of changes in biodiversity per se, i.e., as an inherent characteristic of an ecosystem, we employ a composite metric known as the Biodiversity Intactness Index to capture and communicate the multifaceted nature of biodiversity. However, using complex ecological indices to value abstract concepts might make respondents more susceptible to effects related to the framing of the choice context, thereby raising concerns about validity. Employing a split sample design, we find that value estimates depend on the spatial context in which biodiversity improvements are presented: the larger the spatial scale, the smaller the value. Varying the range of the biodiversity improvement attribute in additional split samples, we find that in two out of the three tested spatial framings, the results are insensitive to the presented attribute range. Respondents thus appear to react to the absolute, rather than the relative, size of the improvements presented. The results from these two spatial framings also exhibit sensitivity to scope, supported by both internal and external scope tests. These findings might alleviate some of the validity concerns associated with employing abstract ecological indices in stated preference valuation studies.