Minimising Payment Vehicle Bias in Contingent Valuation Studies

The payment vehicle is a crucial element inapplications of the contingent valuation methodbecause it provides the context for payment. However,in many countries a relative unfamiliarity with theuse of tax levies and referenda can affect theplausibility of payment vehicles and lead to paymentvehicle bias. The most commonly used approach fordetermining whether payment bias exists is to usetests of convergent validity. It is demonstrated thatsimple tests of convergent validity can be ineffectivein diagnosing the existence of payment vehicle bias.Payment vehicle bias is found to occur because ofdifferences in the coverage of payment vehicles anddoubts about payment being one-off. When respondentsare found to be protesting against a particularpayment vehicle, the current state of the art approachis to delete them from the sample. In this paper analternative approach that relies on the recoding ofprotest responses is proposed.