We conduct, to our knowledge, the first global meta-analysis (MA) of stated preference (SP) surveys of mortality risk valuation. The surveys ask adults their willingness to pay (WTP) for small reductions in mortality risks, deriving estimates of the sample mean value of statistical life (VSL) for environmental, health, and transport policies. We explain the variation in VSL estimates by differences in the characteristics of the SP methodologies applied, the population affected, and the characteristics of the mortality risks valued, including the magnitude of the risk change. The mean (median) VSL in our full data set of VSL sample means was found to be around $7.4 million (2.4 million) (2005 U.S. dollars). The most important variables explaining the variation in VSL are gross domestic product (GDP) per capita and the magnitude of the risk change valued. According to theory, however, VSL should be independent of the risk change. We discuss and test a range of quality screening criteria in order to investigate the effect of limiting the MA to high-quality studies. When limiting the MA to studies that find statistically significant differences in WTP using external or internal scope tests (without requiring strict proportionality), we find that mean VSL from studies that pass both tests tend to be less sensitive to the magnitude of the risk change. Mean VSL also tends to decrease when stricter screening criteria are applied. For many of our screened models, we find a VSL income elasticity of 0.7-0.9, which is reduced to 0.3-0.4 for some subsets of the data that satisfy scope tests or use the same high-quality survey.
Meta-analysis has increasingly been used to synthesise the environmental valuation literature, but only a few test the use of these analyses for benefit transfer. These are typically based on national studies only. However, meta-analyses of valuation studies across countries are a potentially powerful tool for benefit transfer, especially for environmental goods where the domestic literature is scarce. We test the reliability of such international meta-analytic transfers, and find that even under conditions of homogeneity in valuation methods, cultural and institutional conditions across countries, and a meta-analysis with large explanatory power, the transfer errors could still be large. Further, international meta-analytic transfers do not on average perform better than simple value transfers averaging over domestic studies. Thus, we question whether the use of meta-analysis for practical benefit transfer achieves reliability gains justifying the increased effort. However, more meta-analytic benefit transfer tests should be performed for other environmental goods and other countries before discarding international meta-analysis as a tool for benefit transfer.
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Stated preference (SP) surveys have been conducted to value non-timber benefits from forests in Norway, Sweden and Finland for about 20 years. The paper first reviews the literature and summarises methodological traditions in SP research in the three countries. Second, a metaregression analysis is conducted explaining systematic variation in Willingness-to-Pay (WTP). Two important conclusions emerge, with relevance for future research: (1) WTP is found to be insensitive to the size of the forest, casting doubt on the use of simplified WTP/area measures for complex environmental goods; and (2) WTP tends to be higher if people are asked as individuals rather than on behalf of their household.
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