Plausible responsiveness to scope in contingent valuation

Plausible responsiveness to scope is a question of economic significance, in addition to statistical significance, of the scope test in contingent valuation. We briefly review the history of the scope test in order to place the current issue in the context of the BP Deepwater Horizon oil spill. As a result of the review we gain insights into how the issue of scope “adequacy” arose twenty years after it was first mentioned by the NOAA Panel on Contingent Valuation following the Exxon Valdez oil spill. We then provide a review of Desvousges, Mathews and Train (2012) who promote the adding-up test to identify inadequate responsiveness to scope adequacy. The adding-up test is a test of the construct validity of the contingent valuation method but is flawed as a measure of economic significance. We propose scope elasticity of willingness-to-pay as a measure of economic significance. A simulation suggests a likely range of elasticity estimates given linear and quadratic functional forms for the willingness-to-pay function. In order to illustrate the ease of implementation of scope elasticity within the context of the standard scope test we calculate scope elasticity with willingness-to-pay estimates from several studies, describe two studies that directly estimate scope elasticity and estimate scope elasticity with primary data from two studies. All of these empirical estimates of scope elasticity fall within the range of scope elasticity suggested by the simulation. Scope elasticity provides a practical way forward, relative to the adding up test, on the issue of economic significance of scope effects.