The Adding-Up Test in an Incentivized Value Elicitation Mechanism: The Role of the Income Effect

In the context of testing the construct validity of stated preference studies, some researchers advocate the use of an “adding-up test” designed to gauge whether elicited values are sufficiently sensitive to a change in the scope (i.e. size) of a good. Crucial to the applicability of this test in practice, which relies on endowing a subsample of respondents with a good free of charge, is that the income effects due to endowment are negligible. In this study, we apply the adding-up test in an experimental value elicitation format to examine the potential effect of endowment as part of the test design on the adding-up property of elicited values. The results show that the adding-up property can be affected by free provision of part of the bundle.