Nonclassical Experimenter Effects

Experimenter effects denominate effects where an outcome seems to be a result of an experimental intervention but is actually caused by conscious or unconscious effects the experimenter has on how data are produced or processed. This could be through inadvertently measuring one group differently from another one, treating a group of people or animals that are known to receive or to have received the intervention differently compared with the control group, or biasing the data otherwise. Normally, such processes happen inadvertently because of expectation and because participants sense the desired outcome in some way and hence comply or try to please the experimenter. Control procedures, such as blinding (keeping participants and/or experimenters unaware of a study's critical aspects), are designed to keep such effects at ...