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The observer-expectancy effect (also called the experimenter-expectancy effect, expectancy bias, observer effect, or experimenter effect) is a form of reactivity in which a
researcher Research is " creative and systematic work undertaken to increase the stock of knowledge". It involves the collection, organization and analysis of evidence to increase understanding of a topic, characterized by a particular attentiveness ...
's
cognitive bias A cognitive bias is a systematic pattern of deviation from norm or rationality in judgment. Individuals create their own "subjective reality" from their perception of the input. An individual's construction of reality, not the objective input, m ...
causes them to subconsciously influence the participants of an experiment. Confirmation bias can lead to the experimenter interpreting results incorrectly because of the tendency to look for information that conforms to their hypothesis, and overlook information that argues against it. It is a significant threat to a study's
internal validity Internal validity is the extent to which a piece of evidence supports a claim about cause and effect, within the context of a particular study. It is one of the most important properties of scientific studies and is an important concept in reasoni ...
, and is therefore typically controlled using a double-blind experimental design. It may include conscious or unconscious influences on subject behavior including creation of demand characteristics that influence subjects, and altered or selective recording of experimental results themselves.


Overview

The experimenter may introduce cognitive bias into a study in several ways. In what is called the observer-expectancy effect, the experimenter may subtly communicate their expectations for the outcome of the study to the participants, causing them to alter their behavior to conform to those expectations. Such observer bias effects are near-universal in human data interpretation under expectation and in the presence of imperfect cultural and methodological norms that promote or enforce objectivity. The classic example of experimenter bias is that of "
Clever Hans Clever Hans ( German: ''der Kluge Hans''; c. 1895 - c. 1916) was a horse that was claimed to have performed arithmetic and other intellectual tasks. After a formal investigation in 1907, psychologist Oskar Pfungst demonstrated that the horse was ...
", an
Orlov Trotter The Orlov Trotter (also known as ''Orlov;'' Russian: орловский рысак) is a horse breed with a hereditary fast trot, noted for its outstanding speed and stamina. It is the most famous Russian horse. The breed was developed in Ru ...
horse claimed by his owner von Osten to be able to do
arithmetic Arithmetic () is an elementary part of mathematics that consists of the study of the properties of the traditional operations on numbers—addition, subtraction, multiplication, division, exponentiation, and extraction of roots. In the 19th c ...
and other tasks. As a result of the large public interest in Clever Hans, philosopher and psychologist
Carl Stumpf Carl Stumpf (; 21 April 1848 – 25 December 1936) was a German philosopher, psychologist and musicologist. He is noted for founding the Berlin School of Experimental Psychology. He studied with Franz Brentano at the University of Würzburg ...
, along with his assistant Oskar Pfungst, investigated these claims. Ruling out simple fraud, Pfungst determined that the horse could answer correctly even when von Osten did not ask the questions. However, the horse was unable to answer correctly when either it could not see the questioner, or if the questioner themselves was unaware of the correct answer: When von Osten knew the answers to the questions, Hans answered correctly 89% of the time. However, when von Osten did not know the answers, Hans guessed only 6% of questions correctly. Pfungst then proceeded to examine the behaviour of the questioner in detail, and showed that as the horse's taps approached the right answer, the questioner's
posture Posture or posturing may refer to: Medicine * Human position ** Abnormal posturing, in neurotrauma ** Spinal posture ** List of human positions * Posturography, in neurology Other uses * Posture (psychology) In humans, posture can provide a ...
and facial expression changed in ways that were consistent with an increase in tension, which was released when the horse made the final, correct tap. This provided a cue that the horse had learned to use as a reinforced cue to stop tapping. Experimenter-bias also influences human subjects. As an example, researchers compared performance of two groups given the same task (rating portrait pictures and estimating how successful each individual was on a scale of −10 to 10), but with different experimenter expectations. In one group, ("Group A"), experimenters were told to expect positive ratings while in another group, ("Group B"), experimenters were told to expect negative ratings. Data collected from Group A was a significant and substantially more optimistic appraisal than the data collected from Group B. The researchers suggested that experimenters gave subtle but clear cues with which the subjects complied.Rosenthal R. ''Experimenter Effects in Behavioral Research''. New York, NY: Appleton-Century-Crofts, 1966. 464 p.


Prevention

Double blind techniques may be employed to combat bias by causing the experimenter and subject to be ignorant of which condition data flows from. It might be thought that, due to the
central limit theorem In probability theory, the central limit theorem (CLT) establishes that, in many situations, when independent random variables are summed up, their properly normalized sum tends toward a normal distribution even if the original variables themselv ...
of statistics, collecting more independent measurements will improve the precision of estimates, thus decreasing bias. However, this assumes that the measurements are statistically independent. In the case of experimenter bias, the measures share correlated bias: simply averaging such data will not lead to a better statistic but may merely reflect the correlations among the individual measurements and their non-independent nature.


See also

*
List of cognitive biases Cognitive biases are systematic patterns of deviation from norm and/or rationality in judgment. They are often studied in psychology, sociology and behavioral economics. Although the reality of most of these biases is confirmed by reproducible re ...
* Allegiance bias *
Cultural bias Cultural bias is the phenomenon of interpreting and judging phenomena by standards inherent to one's own culture. The phenomenon is sometimes considered a problem central to social and human sciences, such as economics, psychology, anthropology, ...
* Demand characteristics * Epistemic feedback *
Funding bias Funding bias, also known as sponsorship bias, funding outcome bias, funding publication bias, and funding effect, refers to the tendency of a scientific study to support the interests of the study's financial sponsor. This phenomenon is recognized ...
* Hawthorne effect * N rays – imaginary radiation * Naturalistic observation *
Observer bias Observer bias is one of the types of detection bias and is defined as any kind of systematic divergence from accurate facts during observation and the recording of data and information in studies. The definition can be further expanded upon to incl ...
*
Participant observer Participant observation is one type of data collection method by practitioner-scholars typically used in qualitative research and ethnography. This type of methodology is employed in many disciplines, particularly anthropology (incl. cultural an ...
* Placebo and
Nocebo A nocebo effect is said to occur when negative expectations of the patient regarding a treatment cause the treatment to have a more negative effect than it otherwise would have. For example, when a patient anticipates a side effect of a medicatio ...
*
Publication bias In published academic research, publication bias occurs when the outcome of an experiment or research study biases the decision to publish or otherwise distribute it. Publishing only results that show a significant finding disturbs the balance o ...
*
Pygmalion effect The Pygmalion effect, or Rosenthal effect, is a psychological phenomenon in which high expectations lead to improved performance in a given area. The effect is named for the Greek myth of Pygmalion, the sculptor who fell so much in love with the ...
– teachers who expect higher achievement from some children actually get it * Reality tunnel * Reflexivity (social theory) *
Subject-expectancy effect In scientific research and psychotherapy, the subject-expectancy effect, is a form of reactivity that occurs when a research subject expects a given result and therefore unconsciously affects the outcome, or reports the expected result. Because t ...
* Systematic bias * White-hat bias


References


External links


Skeptic's Dictionary on the Experimenter Effect
{{DEFAULTSORT:Observer-Expectancy Effect Design of experiments Cognitive inertia