Michael Perelman asked: >Wasn't Mishan the first to point out the difference between WTP and WTA? An early reference to the concept of WTP vs. WTA is in: Herfindahl, Orris, and Allen Kneese, 1965. "Some Problems Associated with the Use of Rural Areas." Quality of the Environment. Washington: Resources for the Future, Inc., pp. 74-79. Michael Perelman suggests that maybe Mishan said it first. I don't know - when and where did Mishan say it? Either way, it's been around a long time, and should be raised whenever evaluating the Coase (or Stigler?) theorems. Mason Gaffney