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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 the researcher's cognitive bias causes subconscious influence on the participants of the experiment. (i.e. you tend to do what you are expected to do) ^{[see Example]}

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.^[1] It is a significant threat to a study's internal validity, 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.^[2]

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.^[3]

The classic example of experimenter bias is that of "Clever Hans", an Orlov Trotter horse claimed by his owner von Osten to be able to do arithmetic and other tasks. As a result of the large public interest in Clever Hans, philosopher and psychologist Carl Stumpf, 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 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.^[4]

Example

Say you were a popular star singer at your concert, and many of your fans called for a particular song of yours, you tend to choose that as the next song to play, rather than some randomly chosen song.

Say you were the general secretary of the republic, and all of your people cried for "Freedom!", you tend to give them exactly what they want, unless there are some practical reasons prevented you from doing so.

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 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.

References

^ Goldstein, Bruce. "Cognitive Psychology". Wadsworth, Cengage Learning, 2011, p. 374
^ Barry H. Kantowitz; Henry L. Roediger, III; David G. Elmes (2009). Experimental Psychology. Cengage Learning. p. 371. ISBN 978-0-495-59533-5. Retrieved 7 September 2013.
^ Rosenthal, R. (1966). Experimenter Effects in Behavioral Research. NY: Appleton-Century-Crofts.
^ Rosenthal R. Experimenter effects in behavioral research. New York, NY: Appleton-Century-Crofts, 1966. 464 p.

External links

[1] Goldstein, Bruce. "Cognitive Psychology". Wadsworth, Cengage Learning, 2011, p. 374

[KantowitzIII2009-2] Barry H. Kantowitz; Henry L. Roediger, III; David G. Elmes (2009). Experimental Psychology. Cengage Learning. p. 371. ISBN 978-0-495-59533-5. Retrieved 7 September 2013.

[3] Rosenthal, R. (1966). Experimenter Effects in Behavioral Research. NY: Appleton-Century-Crofts.

[4] Rosenthal R. Experimenter effects in behavioral research. New York, NY: Appleton-Century-Crofts, 1966. 464 p.

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@@ Line 1: / Line 1: @@
 {{other uses|Observer effect (disambiguation)}}
 {{psychology sidebar}}
-The '''observer-expectancy effect''' (also called the '''experimenter-expectancy effect''', '''expectancy bias''', '''observer effect''', or '''experimenter effect''') is a form of [[Reactivity (psychology)|reactivity]] in which a [[researcher]]'s [[cognitive bias]] causes them to subconsciously influence the participants of an experiment. [[Confirmation bias]] can lead to the [[experiment]]er interpreting results incorrectly because of the tendency to look for information that conforms to their hypothesis, and overlook information that argues against it.<ref>Goldstein, Bruce. "Cognitive Psychology". Wadsworth, Cengage Learning, 2011, p. 374</ref> It is a significant threat to a study's [[internal validity]], and is therefore typically [[experimental control|controlled]] using a [[double-blind experiment|double-blind experimental design]].
+The '''observer-expectancy effect''' (also called the '''experimenter-expectancy effect''', '''expectancy bias''', '''observer effect''', or '''experimenter effect''') is a form of [[Reactivity (psychology)|reactivity]] in which the [[researcher]]'s [[cognitive bias]] causes subconscious influence on the participants of the experiment. (i.e. you tend to do what you are expected to do) <sup>[see [[#Example|Example]]]</sup>
+[[Confirmation bias]] can lead to the [[experiment]]er interpreting results incorrectly because of the tendency to look for information that conforms to their hypothesis, and overlook information that argues against it.<ref>Goldstein, Bruce. "Cognitive Psychology". Wadsworth, Cengage Learning, 2011, p. 374</ref> It is a significant threat to a study's [[internal validity]], and is therefore typically [[experimental control|controlled]] using a [[double-blind experiment|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.<ref name="KantowitzIII2009">{{cite book|author1=Barry H. Kantowitz|author2=Henry L. Roediger, III|author3=David G. Elmes|title=Experimental Psychology|url=https://books.google.com/books?id=2-5VL8PHLsIC&pg=PA371|accessdate=7 September 2013|year=2009|publisher=Cengage Learning|isbn=978-0-495-59533-5|page=371}}</ref>
@@ Line 15: / Line 17: @@
 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 [[Asch conformity experiments|complied]].<ref>Rosenthal R. ''Experimenter effects in behavioral research''. New York, NY: Appleton-Century-Crofts, 1966. 464 p.</ref>
+== Example ==
+Say you were a popular star singer at your concert, and many of your fans called for a particular song of yours, you tend to choose that as the next song to play, rather than some randomly chosen song.
+Say you were the general secretary of the republic, and all of your people cried for "Freedom!", you tend to give them exactly what they want, unless there are some practical reasons prevented you from doing so.
 ==Prevention==

v t e Biases
Cognitive biases	Acquiescence Ambiguity Anchoring Attentional Attribution Actor–observer Correspondence Authority Automation Availability Mean world Belief Blind spot Choice-supportive Commitment Confirmation Compassion fade Congruence Cultural Distinction Dunning–Kruger Egocentric Curse of knowledge Emotional Extrinsic incentives Fading affect Framing Frequency Frog pond effect Halo effect Hindsight Horn effect Hostile attribution Impact Implicit In-group Illusion of transparency Mean world syndrome Mere-exposure effect Negativity Normalcy Omission Optimism Out-group homogeneity Outcome Overton window Precision Present Pro-innovation Response Restraint Self-serving Social comparison Social influence bias Spotlight Status quo Substitution Time-saving Trait ascription Turkey illusion von Restorff effect Zero-risk In animals
Statistical biases	Estimator Forecast Healthy user Information Psychological Lead time Length time Non-response Observer Omitted-variable Participation Recall Sampling Selection Self-selection Social desirability Spectrum Survivorship Systematic error Systemic Verification Wet
Other biases	Academic Basking in reflected glory Funding FUTON Inductive Infrastructure Inherent In education Liking gap Media False balance Vietnam War Norway South Asia Sweden United States Arab–Israeli conflict Ukraine Net Political bias Publication Reporting White hat
Bias reduction	Cognitive bias mitigation Debiasing Heuristics in judgment and decision-making
Lists: General Memory

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Other	Apophenia Asemic writing Clustering illusion Cryptic crossword Anagram Easter egg Observer-expectancy effect Pattern recognition Palindrome Simulacrum Synchronicity Unconscious mind