In reply Chow et al argue that their data are not subject to verification bias because all screened and enrolled patients underwent ICA irrespective of the computed tomography results. This defense falls short on 2 counts. First, the authors' study comprised 169 patients undergoing coronary angiography among a total of 594 candidates with suspected coronary artery disease. Even if all 169 patients underwent both forms of imaging, the remaining 425 candidates might well exhibit a preferential referral away from diagnostic verification. Without knowing the proportion of positive and negative test responses in all subjects (those referred for verification and those not referred for verification), one cannot determine the presence or degree of verification bias.1 Second, as noted in our Invited Commentary, verification bias depends not only on the test response but also on a variety of concomitant clinical observations (such as the quality and severity of symptoms or the results of other diagnostic tests) that are conditionally correlated with the test under consideration.1,2 Verification bias can still be present if angiographic referral is not conditionally independent of these additional markers. Only random referral toward and away from diagnostic verification (a patently unethical proposal) would prevent this bias. In light of the uncertainties regarding the presence and degree of verification bias in this study, therefore, the optimal range of pretest probability may be very different from the values of 0.10 to 0.86 referred to by the authors. Back to top Article Information Correspondence: Dr Diamond, Division of Cardiology, Cedars-Sinai Medical Center, 2408 Wild Oak Dr, Los Angeles, CA 90068 (firstname.lastname@example.org). Financial Disclosure: None reported. References 1. Diamond GA. Affirmative actions: can the discriminant accuracy of a test be determined in the face of selection bias? Med Decis Making. 1991;11(1):48-562034075PubMedGoogle ScholarCrossref 2. Begg CB, Greenes RA. Assessment of diagnostic tests when disease verification is subject to selection bias. Biometrics. 1983;39(1):207-2156871349PubMedGoogle ScholarCrossref
Archives of Internal Medicine – American Medical Association
Published: Sep 12, 2011
Keywords: ct angiography of coronary arteries
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