Experimenter effect

Social influence or pressure on scientists is external but what about influence from within? It has been known for quite a while that the beliefs and attitudes of the people conducting the experiments affect the results they achieve.

For instance an experimenter may inadvertently treat the experimental groups differently. Also observers coding data or events may unconsciously let bias creep into their scoring. When scientists make mistakes in calculations that fall in with their prediction or hypothesis they are much less likely to notice them than when the mistake stands out against the direction of the hypothesis.

Scientists are under great pressure, putting themselves and their procedures under the microscope in order to remain objective. That means putting their emotions and feelings about their research to one side and conducting their experiments as if they were indifferent to the outcome.