Observer bias

Observer bias is an example of a confounding variable in observational research. Observer bias can occur in that the observer, and thus their results, may be influenced by prior knowledge, or experience of the situation / subject(s) / participant(s) under investigation.
Found on http://www.gerardkeegan.co.uk/glossary/gloss_a.htm

Observer bias

A systematic difference between a true situation and that observed owing to observer variation in perception (ie interpretation).
Found on http://www.cirem.co.uk/definitions.html
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