The subject-expectancy effect is a cognitive bias in scientific research and psychotherapy where a research subject's expectations influence the outcome of an experiment. It occurs when subjects anticipate a specific result, leading them to unconsciously alter their behavior or report outcomes aligned with their expectations. This bias is particularly significant in studies involving human subjects, as it can distort findings and lead to erroneous conclusions.
For instance, a woman visits her doctor who confidently diagnoses her condition and outlines a hopeful treatment plan. Her positive expectations may lead her to experience a placebo effect, enhancing her recovery. Conversely, if the doctor is uncertain and conveys that treatment may or may not work while emphasizing potential negative side effects, the patient’s expectancy may lean towards a nocebo effect, adversely affecting her health outcomes.
To mitigate the subject-expectancy effect, researchers should implement double-blind experimental designs where neither the participants nor the experimenters know the treatment groups, reducing bias in expectations and outcomes.