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
Allan JS, Kanda P, Kennedy RC, Cobb EK, Anthony MS, Eichberg JW. Isolation and characterization of simian immunodeficiency virus from two subspecies of African green monkeys. Aids Res Hum Retrovir. 1990 Mar;6(3):275-85.