VERIFICATION BIAS:
A bias that occurs when some patients in diagnostic screening studies are evaluated with a new experimental test, but not the gold standard (most thorough and accurate) test1,2. Thus, disease status has not been verified in some patients compared to others.
Verification Bias is similar to Workup Bias; although Workup Bias can occur if either the experimental or gold standard test is not completed, and the results are assumed to be equal. Whereas Verification Bias occurs due to a lack of gold standard test results, and the experimental test results are assumed to equal the hypothetical gold standard results.
Verification Bias may lead to an over or underestimate of the accuracy of a new experimental test depending on the variables associated with receiving or not receiving the gold standard test1. For example, if a gold standard test is invasive, or a risky procedure (e.g. biopsy etc.), clinicians may tend to perform the gold standard only on those patients who are likely to have the disease based on previous test results (e.g. positive result on an early test), and avoid it on those who are unlikely to have a disease (e.g. negative result on an earlier test)1.
Some consider Verification Bias to be a non-specific, higher-level concept that describes any biases that involve incomplete or inaccurate diagnoses of patients in routine clinics or studies of diagnosis (e.g. Workup Bias is sometimes considered a type of Verification Bias1). Also see: Workup Bias, Differential Verification Bias, Spectrum Bias, and Information Bias.
References:
1. Porta M, ed. A Dictionary of Epidemiology. Sixth ed. New York, NY: Oxford University Press 2014. (Link to Reference)
2. Richardson ML, Petscavage JM. Verification bias: an under-recognized source of error in assessing the efficacy of MRI of the meniscii. Acad Radiol. 2011;18(11):1376-81. (Link to Reference)