The observer-expectancy effect is a phenomenon in which a researcher's expectations about a given experiment can influence the results. This can occur when the researcher's expectations are communicated to the participants, either directly or indirectly. The effect is most commonly seen in psychological experiments, but can also occur
The observer-expectancy effect is a form of reactivity in which a researcher's cognitive bias causes them to subconsciously influence the participants of an experiment. Confirmation bias can lead to the experimenter interpreting results incorrectly because of the tendency to look for information that affirms their hypothesis, and overlook information that conflicts with it. It is a significant threat to a study's internal validity, and is therefore typically controlled using a double-blind experimental design.