11. De Craen, A.J.M., Moerman, D.E., Heisterkamp, S.H., Tytgate, G.N.J., Tijssen, J.G.P. and Kleijnen, J. (1999). Placebo effect in the treatment of duodenal ulcer, British Journal of Clinical Pharmacology, 48(6), 853-860. doi: 10.1046/j.1365-2125.1999.00094.x