When the subjects of a research change or improve their behaviour not due to a change in the experimental stimulus, it is called

When subjects change or improve their behaviour because they know they are being studied rather than from the stimulus, it is the Hawthorne effect.

The very act of being observed alters how the participants act.

It threatens the validity of experiments by adding an artefact.

The Glenn effect is not a recognised research term here.

The Fisher effect names an economics idea about interest and inflation.

The effect is named after the studies at the Hawthorne Works in the 1920s and 1930s.