Smith VK, Evans MF, Banzhaf HS, Poulos C. Can weak substitution be rehabilitated? Environ Resour Econ (Dordr). 2010 Feb 1;45(2):203-21.
Michels KB, Rothman KJ. Update on unethical use of placebos in randomised trials. Bioethics. 2003 Apr;17(2):188-204.
Mansfield CA. Despairing over disparities: an empirical analysis of the relationship between willingness-to-pay and willingness-to-accept. Environ Resour Econ (Dordr). 1999;13(2):219-34.