Observer Bias

Observer bias occurs when researchers alter the outcome of a study. This process is not typically deliberate, and involves extremely subtle changes both in the way researchers interact with subjects in the study and in what observers choose to see.

What Causes Observer Bias?
Most researchers know what they are studying. For example, a teacher conducting a study of math skills in girls and boys knows that he or she is comparing girls and boys. This can subtly influence his/her behavior because he/she expects that there will be some difference between girls and boys. The teacher may also have a hypothesis about the outcome, which could affect what he/she chooses to see. For example, a teacher who believes boys are better at math is more likely to notice boys’ math skills and fail to notice their deficiencies.

Similarly, when researchers interact with subjects they may subtly alter the outcome of the research. The teacher studying differences in math skills between boys and girls might spend more time teaching boys because he/she believes that boys are better at math. This, in turn, makes it more likely that boys will effectively learn math and can alter the outcome of the study. Subtle prejudices can also influence the conclusions the teacher draws. The teacher might, for example, notice girls studying very hard and outperforming boys. Rather than concluding that math skills are correlated with time spent studying, the teacher might argue that girls are less good at math than boys because they have to spend more time studying.

How Can Researchers Correct for Observer Bias?
The most effective way to avoid observer bias is to use double blind studies, where neither the researcher nor the subjects know what is being studied. This, however, is often impossible in psychological research. Researchers who are aware of their biases going into an experiment and who make efforts to correct these biases may avoid some bias. When researchers do not have a financial investment in a particular outcome they are also less likely to be biased.

Observer Bias Scrutiny
Many researchers have claimed that observer bias has contributed to differences in behavior and performance between races and genders in scientific studies. Ape language studies have also been roundly criticized because the people teaching apes sign language are also typically the people testing performance, and therefore have a vested interest in the outcome of the research.


  1. Colman, A. M. (2006). Oxford dictionary of psychology. New York, NY: Oxford University Press.

Last Updated: 08-12-2015

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