Also known as the observer effect, this refers to the influence that scientists who conduct an experiment have on the performance of participants and the interpretation of the results. It is a form of bias that affects the validity of experiments as the scientists, either deliberately or otherwise, influence the test results. It is one of the reasons why the results of many scientific studies do not get replicated by future studies, and good scientists look for various ways to negate it. The concept was elaborated by Robert Rosenthal in Experimenter Effects in Behavioral Research.