WORKUP BIAS:
Bias due to incorrectly or incompletely diagnosed patients being more numerous in one study group compared to another1. Also called Partial Verification Bias2 (synonym) or considered a type of Verification Bias1.
Workup Bias usually occurs when some patients receive more thorough diagnostic screening compared to others. For example, patients who are found to be negative on a preliminary screening test may not receive a second, more thorough, screening test later1. Whereas, those who are positive on the preliminary test may receive a more thorough test later to confirm (verify) the diagnosis.
Workup Bias occurs in diagnostic screening studies when a new experimental screening test is compared to a gold standard (thorough, more accurate) test, but not all participants in the study receive both tests. Workup Bias may over or underestimate the accuracy of a new experimental test depending on the ratio of positive vs. negative results observed on the experimental test. This over or underestimate occurs when the results from a experimental test are assumed to equal the results of the gold standard test; despite one of the tests not actually being completed.
Diagnostic screening studies which use pre-existing data from medical charts, obtain from routine clinics, may be most at risk of Workup Bias, because in typical, routine clinical settings, not all patients typically receive multiple tests to diagnose some diseases. This lack of thorough verification in routine clinics may be especially evident for diseases which are not considered serious or life threatening. Also see: 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. de Groot JA, Dendukuri N, Janssen KJ, Reitsma JB, Brophy J, Joseph L, Bossuyt PM, Moons KG. Adjusting for partial verification or workup bias in meta-analyses of diagnostic accuracy studies. Am J Epidemiol. 2012;175(8):847-53. (Link to Reference)