In a few surveys, however, researchers explicitly inquired about both WTP and WTA. The answers have diverged far more than theory would suggest.21 Economists have been skeptical in response to the divergence,
suggesting that several types of errors affect the results. Such errors include:(1) strategic responses, where the respondents lie to the surveyor in an effort to manipulate the outcome in accord with the respondents' true preferences; (2) information biases, where the surveyors (perhaps inadvertently) manipulate the responses by supplying information about the proposed program; (3) instrument biases, where the surveyors' questioning techniques mold the results; and (4) errors produced by nonrandom sampling techniques.22 In the last few years, some experime