The expectancy effect (or experimenter effect) arises in science when a researcher or subject expects a given result and therefore unconsciously manipulates an experiment or misinterprets data in order to find it. The effect is so powerful that the expensive and complex double blind methodology is needed to combat it. What is science? There are different theories of what science is. ... Double-blind describes an especially stringent way of conducting an experiment, usually on living, conscious, human subjects. ...

It is often a cause of "odd" results in many fringe experiments, notably in paranormal investigation. One example was the horse Clever Hans, who seemed to be performing arithmetic, but in reality took unconscious cues from his trainer. At another time children were given rats and told that some were bred for intelligence, some for dullness. In reality, the rats were chosen at random, but the children reported that the "smart" rats learned mazes faster. Anomalous phenomena are phenomena which are observed and for which there are no suitable explanations in the context of a specific body of scientific knowledge, e. ... Clever Hans performs Clever Hans (in German, der Kluge Hans) was a horse that was apparently trained to perform arithmetic and other intellectual tasks. ... Arithmetic or arithmetics (from the Greek word αριθμός = number) in common usage is a branch of (or the forerunner of) mathematics which records elementary properties of certain operations on numerals, though in usage by professional mathematicians, it often is treated as synonym for number theory. ...

Another example of the theory can be demonstrated in the more recent activity of music backtracking. Some people expect to hear hidden messages when reversing songs, and therefore hear the messages. To others these may sound nothing more than random sounds. A backward message (otherwise, but incorrectly, known as Backmasking) is a supposed message hidden in an audio recording that is only fully apparent when played backwards. ...

External links and references

• Skeptic's Dictionary on the Experimenter Effect (http://skepdic.com/experimentereffect.html)
• The rat study (http://www.midtermpapers.com/view.php/d/1381.htm)
• An article that speaks of Expectancy effects in paranormal investigation (http://www.williamjames.com/Science/ESP.htm)
• Another article by Rupert Sheldrake (http://www.sheldrake.org/experiments/expectations/)