experimenter effect
any influence a researcher may have on the results of his or her research, derived from either interaction with participants or unintentional errors of observation, measurement, analysis, or interpretation. In the former, the experimenter’s personal characteristics (e.g., age, sex, race), attitudes, and expectations directly affect the behavior of participants. In the latter, the experimenter’s procedural errors (often arising from his or her expectations about results) have no effect on participant responses but indirectly distort the research findings.