Contingent valuation with an open-ended follow-up question: a test of scope effects.

It has been suggested that an open-ended follow-up question should be added to the binary contingent valuation question. Before this is generally recommended, it is important to evaluate the properties of such follow-up questions. Using a split sample approach, we test whether the open-ended follow-up is sensitive to the scope of the commodity being valued. No significant scope effects were detected. It is concluded that the results obtained do not support the use of an open-ended follow-up in contingent valuation applications.