Kim D, Lauria DT, Poulos C, Dong B, Whittington D. Effect of travel distance on household demand for typhoid vaccines: implications for planning. Int J Health Plann Manage. 2013 Mar 12;Advance Online.
Michels KB, Rothman KJ. Update on unethical use of placebos in randomised trials. Bioethics. 2003 Apr;17(2):188-204.
Mansfield CA. A consistent method for calibrating contingent value survey data. South Econ J. 1998;64(3):665-81.