Subject-expectancy effect

The Subject-expectancy effect, in science, is a cognitive bias that occurs in science when a subject expects a given result and therefore unconsciously affects the outcome of an experiment or treatment, 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. The Subject-expectancy effect is most commonly found in medicine, where it can result in the subject experiencing the Placebo effect or nocebo effect, depending on how the influence pans out.

An example of a scenario involving these various effects is as follows: A woman goes to her doctor with an issue. The doctor diagnoses with certainty, and 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 in her recovery. On the other hand, if her doctor had had little time for her, was uncertain about the diagnosis, and had given her a prescription, combined with a message along the lines of, "this may help sometimes," and added a message about possible horrible side effects (combined, say, with the patient having talked to a neighbor who also speaks along the same lines about the horrible side effect), then the chance of negative subject-expectancy, or nocebo, becomes quite large. The subject expectancy effect is also clearly seen in psychotherapy.