Introduction: The nature of the object of inquiry and difficulties for causal inference

Fisher first employed his technique of randomization, together with the theory of causal inference formalized in the previous chapter, in agricultural experiments, where the group members were fields, or sections of fields, of crops, and the treatments were various sorts or amounts of soil enrichment or fertilizer. Only with concepts of “field” and “crop” radically at odds with common sense, then, could we say that Fisher's objects of inquiry were conscious or willful. Within a few decades of its introduction, though, randomization became a standard feature of biomedical drug-testing experiments, where the group members are human subjects and the treatments are various sorts or amounts of drugs. Thus, the human subjects of such drug-testing experiments are certainly conscious, in any ordinary sense of the term, and also creatures of will.

Physicians had early recognized that subject awareness in a medical experiment in which subjects had to be relied on to report results might lead to difficulties. For example, knowledge that they were taking a new aspirin tablet might lead subjects to report greater relief from their headache conditions than had actually occurred. To counteract such misreporting, physicians employ a so-called double-blind experiment, in which a treatment group receives the aspirin, and the control group gets a “placebo,” and neither subjects nor physicians know which group subjects are in. Recent historical research illuminates the origin of such techniques: