The tendency of researchers to subtly and inadvertently affect the behaviour of participants in a study, obscuring the true effect of the independent variable, refers to:

Experimental bias occurs when a researcher unintentionally influences participants and distorts the genuine effect of the independent variable.

It reflects the experimenter's own expectations leaking into the study through tone, cues or scoring.

Hawthorne effect is the change in participants caused by their awareness of being observed, not by the researcher.

Biosocial effect refers to bias arising from the researcher's biological traits like age, sex or race.

Participant bias covers distortions produced by the respondents themselves, such as social desirability.

Double-blind designs are used to control experimenter and participant expectancy together.