John Henry effect

n. A concept related to experimental validity; the term describes the phenomenon of special effort put forth by the control group in a research study. In an experiment in which the assignment of experimental and control conditions is made public and the control group will be at a disadvantage if a treatment is successful, the control group may be motivated to reduce any expected differences. Just as John Henry, the steel drivin‘ man, put forth extra effort in his desire to outperform a steam drill, under some conditions control group members may do likewise. For example, a company may wish to test the efficiency of automating production. If the employees perceive their jobs to be threatened if the test for efficiency shows the automated process to be superior to human performance, they may work at peak efficiency during the comparison period so as to minimize any overall differences in performance.

- TJM