What is bias and confounding and why are they important?

Robert Larson, DVM, PhD, DACT, DACVPM (Epidemiology), DACAN

Professor, Production Medicine; Edgar E. and M. Elizabeth Coleman Chair Food Animal Production Medicine; Executive Director, Veterinary Medical Continuing Education; College of Veterinary Medicine, Kansas State University

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Well-designed studies differ from clinical experience because explicit constraints are implemented to control for sources of bias. Clinical experience is particularly prone to bias because the same person provides and then evaluates interventions. Biases that occur commonly, and often inadvertently, when relying on clinical experience are typically grouped into categories of selection bias, information bias, and confounding.

Observations in clinical settings are plagued by selection bias because although this bias is a crucial flaw if one wants to compare interventions, it is perfectly appropriate and beneficial when applied to clinical case management. Essentially, selection bias occurs when animals with certain signalment, history, or physical examination findings are treated differently than animals without those case characteristics. While clinically reasonable, this practice prevents any attempt to accurately compare alternative risks or treatments.

Similarly, information bias is very common in clinical case management because we intentionally gather different types and amounts of information about different animals. For example, it is reasonable to observe some animals more closely, under different circumstances, or for longer periods of time than other animals. However, this bias can lead to incorrect associations with either disease-causation or treatment factors.

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