Watson V, Ryan M. Exploring preference anomalies in double bounded contingent valuation. J Health Econ. 2007 May 1;26(3):463-82. doi: 10.1016/j.jhealeco.2006.10.009
Cassingham KM, Sills EO, Pattanayak SK, Mansfield CA. Voluntary conservation of North Carolina's natural heritage. J For. 2002;100(5):16-23.