In epidemiological research, recall bias is a systematic error caused by differences in the accuracy or completeness of the recollections retrieved ("recalled") by study participants regarding events or experiences from the past.[1] It is sometimes also referred to as response bias, responder bias or reporting bias.


Recall bias is a type of measurement bias, and can be a methodological issue in research involving interviews or questionnaires. In this case, it could lead to misclassification of various types of exposure.[2] Recall bias is of particular concern in retrospective studies that use a case-control design to investigate the etiology of a disease or psychiatric condition.[3][4][5] For example, in studies of risk factors for breast cancer, women who have had the disease may search their memories more thoroughly than members of the unaffected control group for possible causes of their cancer. Those in the case group (those with breast cancer) may be able to recall a greater number of potential risk factors they had been exposed to than those in the control group (women unaffected by breast cancer). This can potentially exaggerate the relation between a potential risk factor and the disease.[6]


To minimize recall bias, some clinical trials have adopted a "wash out period", i.e., a substantial time period that must elapse between the subject's first observation and their subsequent observation of the same event.[7] Use of hospital records rather than patient experience can also help to avoid recall bias.[8] Standardising sampling methods can help to avoid needing recall information in the first place.[9]

Often, recall bias is difficult to avoid, and many studies change experiment design to avoid recalling information.[9]


  1. ^ Last, John M, ed. (30 November 2000). A Dictionary of Epidemiology. Oxford University Press. p. 153. ISBN 978-0-19-977434-0. Retrieved 28 March 2013.
  2. ^ Moren, Alain; Valenciano, Marta (Kitching, Aileen, ed.). "Information (measurement) bias". Field Epidemiology Manual. FEM Wiki. Archived from the original on 2019-08-18. Retrieved 28 March 2013.((cite web)): CS1 maint: multiple names: authors list (link)
  3. ^ Kopec, JA; Esdaile, JM (September 1990). "Bias in case-control studies. A review". Journal of Epidemiology and Community Health. 44 (3): 179–86. doi:10.1136/jech.44.3.179. PMC 1060638. PMID 2273353.
  4. ^ Prince, Martin (2012-01-01), Wright, Pádraig; Stern, Julian; Phelan, Michael (eds.), "9 - Epidemiology", Core Psychiatry (Third Edition), Oxford: W.B. Saunders, pp. 115–129, doi:10.1016/b978-0-7020-3397-1.00009-4, ISBN 978-0-7020-3397-1, retrieved 2020-10-21
  5. ^ Hoang, Van Dong; Tran, Van Dinh; Lee, Andy H. (2015-01-01), Preedy, Victor R. (ed.), "Chapter 39 - Coffee Consumption and Prostate Cancer", Coffee in Health and Disease Prevention, San Diego: Academic Press, pp. 359–366, doi:10.1016/b978-0-12-409517-5.00039-5, ISBN 978-0-12-409517-5, retrieved 2020-10-21
  6. ^ Schulz, KF; Grimes, DA (February 2, 2002). "Case-control studies: research in reverse" (PDF). Lancet. 359 (9304): 431–4. doi:10.1016/S0140-6736(02)07605-5. PMID 11844534. S2CID 10770936. Archived from the original on June 15, 2016.((cite journal)): CS1 maint: bot: original URL status unknown (link)
  7. ^ Mukhopadhyay, Sanjay; Feldman, Michael; Abels, Esther (2017). "Whole slide imaging versus microscopy for primary diagnosis in surgical pathology: a multicenter randomized blinded noninferiority study of 1992 cases (pivotal study)". American Journal of Surgical Pathology. 42 (1): 39–52. doi:10.1097/PAS.0000000000000948. PMC 5737464. PMID 28961557.
  8. ^ Lee, William; Hotopf, Matthew (2012-01-01), Wright, Pádraig; Stern, Julian; Phelan, Michael (eds.), "10 - Critical appraisal: Reviewing scientific evidence and reading academic papers", Core Psychiatry (Third Edition), Oxford: W.B. Saunders, pp. 131–142, doi:10.1016/b978-0-7020-3397-1.00010-0, ISBN 978-0-7020-3397-1, retrieved 2020-10-21
  9. ^ a b Torelli, Paola; Jensen, Rigmor (2010-01-01), Aminoff, Michael J.; Boller, François; Swaab, Dick F. (eds.), "Chapter 10 - Headache diaries and calendars", Handbook of Clinical Neurology, Headache, 97, Elsevier: 137–146, doi:10.1016/s0072-9752(10)97010-3, ISBN 9780444521392, PMID 20816416, retrieved 2020-10-21