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Observer Expectancy Effect. The observer expectancy effect, also called the experimenter expectancy effect, is a phenomenon that can occur when a researcherâs beliefs or expectations cause him or her to unconsciously influence the participants of an experiment. In order to conserve the internal validity of an experiment, researchers can use a double-blind experimental design.
A number of factors can affect the outcome of any type of experimental research. One is finding samples that are random and representative of the population being studied. Another is experimenter bias, in which the researcher's expectations about what should or should not happen in the study sway the results.