The observer-expectancy effect (also called the experimenter-expectancy effect, observer effect, or experimenter effect) is a form of reactivity, in which a researcher's cognitive bias causes them to unconsciously influence the participants of an experiment. It is a significant threat to a study's internal validity, and is therefore typically controlled using a double-blind experimental design.

An example of the observer-expectancy effect is demonstrated in music backmasking, in which hidden verbal messages are said to be audible when a recording is played backwards. Some people expect to hear hidden messages when reversing songs, and therefore hear the messages, but to others it sounds like nothing more than random sounds. Often when a song is played backwards, a listener will fail to notice the "hidden" lyrics until they are explicitly pointed out, after which they are obvious. Other prominent examples include facilitated communication, dowsing, and applied kinesiology.

See also

• Clever Hans - a horse who seemed to be performing arithmetic and other amazing skills, but in reality took cues transmitted unconsciously by his trainer and observers.
• Placebo - an inert medicine or preparation which works because the patient thinks it will
• N-rays - imaginary radiation
• Pygmalion effect - teachers who expect higher achievement from some children, actually get it
• Reflexivity (social theory)
• Subject-expectancy effect
• Nocebo

External links and references

• Skeptic's Dictionary on the Experimenter Effect
• The rat study
• An article that speaks of Expectancy effects in paranormal investigation
• Another article by Rupert Sheldrake
• Songs of Praise (With subtitles) An example of observer-expectancy effect involving subtitles which alter the observer's interpretation of audio.