John Henry Effect

The John Henry effect refers to the bias introduced to an experiment when members of the control group are aware that they are being compared to the experimental group and behave differently than they typically would to compensate for their perceived disadvantage. This alteration renders the control group ineffective as a measure of baseline performance and skews the results of the experiment. The John Henry effect is also associated with resistance to change and innovation, which may be perceived as disruptive or threatening to the present status of members of the control group. This entry describes the John Henry effect’s origins and potential implications for research into innovations in education.


The John Henry effect is named after legendary American folk hero John Henry, a steel driver ...

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