Michels KB, Rothman KJ. Update on unethical use of placebos in randomised trials. Bioethics. 2003 Apr;17(2):188-204.
Hartman M, Bolton E, Fehnel SE. Accounting for age differences on the Wisconsin Card Sorting Test: decreased working memory, not inflexibility. Psychol Aging. 2001 Sep 1;16(3):385-99.