Observer bias

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In research, observer bias is a form of detection bias originating at a study's stage of observing or recording information.[1] Different observers may assess subjective criteria differently,[2] and cognitive biases (including preconceptions and assumptions) can affect how a subject is assessed.[3] For example, being aware of a subject's disease status may introduce a bias in how the outcome is assessed.[4] Observer bias can also occur when the subject knows they are being examined. When a subject knows they are being observed, it can cause them to act different to how they normally would, which could interfere with the experiment. [5]Another example examines police work, where police officers change their behavior based on who is watching.[6]

Blinded experiments are used to limit observer bias.[1] Observer bias can also be avoided or limited by having researchers work independently of one another.[7]


  1. ^ a b Mahtani, Kamal; Spencer, Elizabeth A; Brassey, Jon; Heneghan, Carl (2018). "Catalogue of bias: observer bias". BMJ Evidence-Based Medicine. 23 (1): 23–24. doi:10.1136/ebmed-2017-110884. ISSN 2515-446X. Observer bias is any kind of systematic discrepancy from the druth during the process of observing and recording information for a study. Observer bias is a type of detection bias [...]
  2. ^ Hróbjartsson, Asbjørn; Thomsen, Ann Sofia Skou; Emanuelsson, Frida; Tendal, Britta; Hilden, Jørgen; Boutron, Isabelle; Ravaud, Philippe; Brorson, Stig (2012-02-27). "Observer bias in randomised clinical trials with binary outcomes: systematic review of trials with both blinded and non-blinded outcome assessors". BMJ. 344: e1119. doi:10.1136/bmj.e1119. ISSN 0959-8138. PMID 22371859.
  3. ^ "Observer Bias", The SAGE Encyclopedia of Social Science Research Methods, Sage Publications, doi:10.4135/9781412950589.n651, ISBN 9780761923633
  4. ^ Brown, Louise (2010), Bennett, Phillip; Williamson, Catherine (eds.), "Chapter Fourteen - Statistics and evidence-based healthcare", Basic Science in Obstetrics and Gynaecology (Fourth Edition), Churchill Livingstone, pp. 289–304, doi:10.1016/b978-0-443-10281-3.00018-x, ISBN 9780443102813, Observer bias occurs when the investigator is aware of the disease status, treatment group or outcome of the subject and their ability to interview the subject, collect or analyse the data in an unbiased manner is compromised.
  5. ^ White, J. H., Hegarty, J. R., & Beasley, N. A. (1970). Eye contact and observer bias: A research note. British journal of Psychology, 61(2), 271.
  6. ^ Spano, R. (2005). Potential sources of observer bias in police observational data. Social science research, 34(3), 591-617
  7. ^ Burghardt, G. M., Bartmess‐LeVasseur, J. N., Browning, S. A., Morrison, K. E., Stec, C. L., Zachau, C. E., & Freeberg, T. M. (2012). Perspectives–minimizing observer bias in behavioral studies: a review and recommendations. Ethology, 118(6), 511-517.

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