Observer-expectancy effect

The observer-expectancy effect^[a] is a form of reactivity in which a researcher's cognitive bias 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.^[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 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.^{[citation needed]}

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.^{[citation needed]} 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]

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.

Notes

^ Also called the experimenter-expectancy effect, expectancy bias, observer effect, or experimenter effect.

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

Skeptic's Dictionary on the Experimenter Effect

[1] Also called the experimenter-expectancy effect, expectancy bias, observer effect, or experimenter effect.

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

[KantowitzIII2009-3] 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.

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

[5] Rosenthal R. Experimenter Effects in Behavioral Research. New York, NY: Appleton-Century-Crofts, 1966. 464 p.

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v t e Biases
Cognitive biases	Acquiescence Ambiguity Affinity 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 Proximity 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 Déformation professionnelle 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

v t e Hidden messages
Main	Subliminal message
Audio	Backmasking list Hidden track list pregap list Phonetic reversal Reverse speech
Numeric	Chronogram Numerology Theomatics Bible code Cryptology
Visual	Fnord Hidden text Paranoiac-critical method Pareidolia Psychorama Sacred geometry Steganography Visual cryptography
Other	Apophenia Asemic writing Clustering illusion Cryptic crossword Anagram Easter egg Observer-expectancy effect Pattern recognition Palindrome Simulacrum Synchronicity Unconscious mind

Overview

Prevention

Notes

See also

References

External links