¥ Respondents may make associations among
environmental goods that the researcher had not intended. For example, if
asked for willingness to pay for improved visibility (through reduced
pollution), the respondent may actually answer based on the health risks
that he or she associates with
dirty air.
¥ Some researchers argue that there is a fundamental difference
in the way that people make hypothetical decisions relative to the way they make actual decisions. For example, respondents may fail to take questions
seriously because they will
not actually be required to pay the stated amount. Responses may be unrealistically high if respondents believe they will not have to
pay for the good or service and that their answer may influence the resulting supply of the good. Conversely,
responses may be unrealistically low if respondents believe they will have to pay.
¥ The payment question can either be phrased as the
conventional ÔWhat are you willing to pay (WTP) to receive this environmental
asset?Õ, or in the less usual form, ÔWhat are you willing to accept (WTA) in compensation for
giving up this environmental asset?Õ In theory, the results should be very
close. However, when the two formats have been compared, WTA
very significantly exceeds WTP. Critics have
claimed that this result invalidates the CVM approach,
showing responses to be expressions of what individuals would like to have
happen rather than true valuations.
¥ If people are first asked for their willingness to pay for
one part of an environmental asset (e.g. one lake in an entire system of lakes) and then asked to value
the whole asset (e.g. the whole lake system), the amounts stated may be similar. This is
referred to as the Òembedding effect.Ó
¥ In some cases, peopleÕs expressed willingness to pay for
something has been found to depend on where it is placed on a list of
things being valued. This is referred to as the "ordering problem."
¥ Respondents may give different willingness to pay amounts,
depending on the specific payment vehicle chosen. For example, some payment vehicles, such as taxes, may lead
to protest responses from people who do not want increased taxes. Others, such as a contribution or donation, may lead people
to answer in terms of how much they think their Òfair shareÓ contribution
is, rather than expressing their actual value for the good.
¥ Many early studies attempted to prompt respondents by
suggesting a starting bid and then increasing or decreasing this bid based upon whether the
respondent agreed or refused to pay a such sum. However, it has been shown that the choice of starting bid affects
respondents final willingness to pay response.