john henry effect

Definition:
John Henry effect: Bias due to a perceived threat or similar negative perception that influences control groups' performance.

The John Henry effect is a common biases in research design that can occur in social experiments if members of a control group are aware of their status and are able to actively work harder to overcome the "disadvantage" of being in the control group, thus skewing results of the study. (Wikipedia)

Suter, W. (2012). Ch. 7, pg. 186-216. Introduction to Educational Research: A Critical Thinking Approach. SAGE Publications, Inc.https://doi.org/10.4135/9781483384443