Subject-expectancy effect
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The Subject-expectancy effect, in science, is a cognitive bias that occurs in science when a subject expects a given result and therefore unconsciously manipulates an experiment or reports the expected result. Because it can skew the results of experiments (especially on human subjects), double-blind methodology is used to eliminate the effect.
Like the Observer-expectancy effect, it is often a cause of "odd" results in many experiments. But the Subject-expectancy effect is most commonly found in medicine, where it is called the Placebo effect or nocebo effect, depending on how the influence pans out.
An example would this would be as follows: a woman goes to her doctor with an issue. The doctor diagnoses with certainty, then clearly explains the diagnosis and the expected route towards recovery. If he does this convincingly, calming her, removing fear and installing hope, she will likely through the positive expectancy experience the placebo effect, aiding her recovery. On the other hand, if her doctor has little time for her, is uncertain about the diagnosis, gives her a prescription combined with a message along the lines of, "this may help sometimes," and adds a message about the horrible side effects (combine this with talking to a neighbor who says more along the same lines about the horrible side effect), the chance of negative subject-expectancy, or nocebo, becomes quite large.
The subject expectancy effect is also clearly seen in psychotherapy.
