Statistics and Probability Dictionary
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if subjects in the
know that they are receiving a
the placebo effect will be reduced or eliminated; and
the placebo will not serve its intended control purpose.
Blinding is the practice of not telling
subjects whether they are receiving a placebo. In this
way, subjects in the control and treatment groups
experience the placebo effect equally. Often, knowledge
of which groups receive placebos is also kept from
analysts who evaluate the experiment. This practice
is called double blinding. It prevents the
analysts from "spilling the beans" to subjects through
subtle cues; and it assures that their evaluation is not
tainted by awareness of actual treatment conditions.