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  • Intentional Ignorance: A History of Blind Assessment and Placebo Controls in Medicine
  • Ted J. Kaptchuk* (bio)


Blind assessment is considered a critical component of modern medical research methodology. Nonetheless, attention to this practice in the historiography of human experimentation has varied from nil to minimal, occupying at most a few short paragraphs in a relatively few articles and books. Such brief, perfunctory accounts as do exist portray it as having been adopted after World War II following, at most, a few precursors. In addition, the details of these accounts are surprisingly inconsistent, and the rationale for blind assessment is presented as self-evident and devoid of social or historical dimensions. 1 The history of masked [End Page 389] assessment seems veiled in obscurity, with the implication that this method was not available until well into the twentieth century, when an eternal transhistorical scientific verity somehow became obvious to researchers. The aura of objectivity and neutrality attached to blind assessment itself may have benefited from this absence of a past.

In fact, however, blind assessment has been a continuous and complex scientific and social enterprise for more than two hundred years. The testing of human subjects under conditions of intentional ignorance has taken numerous forms. The simplest method was to use blindfolds or curtains so that the patient (and/or the experimenter) was unaware of the exact nature or timing of the intervention. The veil helped to eliminate the threat of imagination and bias, and sometimes it served as insurance against fraud and trickery. From its very inception, blind investigation also utilized a decoy or dummy intervention (such as a placebo or sham device) that allowed researchers to observe the effects of the appearance of intervention. 2 Blind assessment could also be “double-blind” [End Page 390] (to use the modern phrase), so that both the patient and the experimenter were unaware of whether the treatment was ritual alone or a ritual that included the experimental therapy. In any of its forms, and in all of them taken together, blind investigation helped medical science isolate “hard” knowledge and material causality from the contamination of mental delusion, enthusiastic bias, or even calculated deceit.

This essay examines the unacknowledged saga of a research methodology that placed a higher value on information derived from people who were kept “ignorant” during an assessment. It concerns the study of living human beings. Most of the story is medical, but it also touches related research with human subjects in psychology and pharmacology, research that needed the guarantee of concealment. Its leitmotif is noble conflict and intellectual doubt. Its intent is to wrest certainty out of the shadows of human awareness. The test is an ordeal of darkness. The unspoken countertheme of human passions is revealed in the details of circumstances and timing: When was it critical to distinguish material causality from its mere appearance? When was fraud or suggestion through other sensory or mental pathways a lurking threat? When were seeing and feeling not to be believed? When did objective truth need to be protected from the contamination of the mind?

I will trace the development of blind assessment by examining the most representative episodes of its use up until its widespread acceptance in biomedical research. The story can be roughly divided into five phases. Blind assessment began in the late eighteenth century as a tool for detecting fraud in a campaign mounted by elite mainstream scientists and physicians to challenge the suspected delusions or charlatanism of unconventional medicine. It demarcated orthodox medicine from what was considered deviant healing. In the second phase, beginning in the mid-nineteenth century, blind assessment became a research tool within various medical communities. Often this utilization was a defensive adaptation by proponents of irregular healing, but some conventional physicians in other situations also employed it for polemical medical display. The third phase began in the late nineteenth century when experimental psychologists tried to separate the private and unquantifiable components of the mind from the objective and quantifiable components of sensation and perception. Psychical researchers sought to bolster shaky scientific identity with concealed experimentation. Most critically, blind assessment also became a decisive vehicle by which neurologists and psychiatrists could demarcate the...

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pp. 389-433
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