Among the most important tasks for a CV analysis are questionnaire design and survey
procedure (Haab and McConnell, 2001). The CV method uses surveys in which people are asked
how much they are willing to pay for a change in the condition of some environmental resources
or a service that is meaningful to the respondent in a hypothetical situation (Diamond, et. al.,
1993; Haab and McConnell, 2001). Early CV designs involve open-ended question such as,
“What is the maximum amount you would pay for...?” More recently, the commonly used
methods include iterative bidding, payment cards, and dichotomous choice questions. Several
studies reveal that different techniques of asking CV questions provide significantly different
estimates of Hicksian surplus (Boyle and Bishop, 1988).
In this study, the CV is employed to estimate the WTP for non-GM food products. The
CV scenario in the survey conducted in this study contains both the dichotomous choice and
polychotomous choice questions. Food products used in the survey include vegetable oil, salmon,
and corn flake breakfast cereal. Vegetable oil and corn flake breakfast cereal used a dichotomous
response question, as the respondents were asked to choose between GM and non-GM
alternatives given the price scenario. For salmon, a polychotomous response question was
designed, as surveyed respondents were asked to rank within three different types of GM, non-
GM but fed with feed containing GM corn or soybeans, and non-GM fed with non-GM feed
alternatives. In this study, we only analyze a model for the dichotomous choice between GM and
non-GM products. Thus, the GM salmon and GM-fed salmon are combined as the same category
in this study.
The Random Utility Model
We adopt a random utility model for analyzing dichotomous CV responses. Following
Haab and McConnell (2001), the indirect utility function for respondent j can be written as: