Rethinking the scope test as a criterion for validity in contingent valuation

Abstract

The scope test is widely recommended as a way to evaluate the validity of contingent valuation (CV) studies. We measured contingent values of parts and wholes for four different environmental goods and applied the conventional scope test. In addition, the study design allowed examination of scope relationships for individual respondents. We also used social psychological theory to expand the definition of scope to include attitudinal and behavioral scope. Looking at the individual responses showed that conventional economic scope test results, which depend on comparisons of average values, can hide important relationships that are relevant to the validity of CV studies. We showed that, as a validity test, the conventional scope test can lead to false positives and false negatives. We are led to question the efficacy and cost effectiveness of making scope tests a routine part of validity assessment in applied CV studies.