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Impact of Verification Bias

Michael S. Lauer, MD; Sudish C. Murthy, MD, PhD; Eugene H. Blackstone, MD; Ikenna C. Okereke, MD; Thomas W. Rice, MD

Arch Intern Med. 2007;167(2):161-165.

Background  Verification bias occurs when test findings influence the decision to perform a gold standard test. It adversely influences diagnostic test accuracy by inflating sensitivity and deflating specificity. We studied the impact of verification bias on the estimated accuracy of a test commonly used in suspected lung cancer.

Methods  We studied 534 consecutive patients referred for [¹⁸F]fluorodeoxyglucose uptake by positron emission tomography (PET). Primary outcomes were tissue diagnoses of cancer and of mediastinal lymph node metastases. A secondary outcome was 3-year mortality. We accounted for verification bias using 2 validated methods.

Results  The gold standard test, namely tissue acquisition, was performed in 419 patients (78%); mediastinal lymph node sampling occurred in 301 (56%). While the 410 patients with PET-diagnosed stage I cancer or higher were more likely than patients with negative PET scan findings to undergo tissue diagnosis testing (92% vs 34%) (P<.001), there was no association between PET findings and performance of mediastinal sampling. Without accounting for verification bias, the sensitivity and specificity of PET for diagnosis of cancer were 0.95 (95% confidence interval [CI], 0.92-0.97) and 0.31 (95% CI, 0.21-0.42), respectively. After adjustment, sensitivity fell to 0.85 (95% CI, 0.81-0.89), while specificity increased to 0.51 (95% CI, 0.40-0.60). For diagnosis of mediastinal disease, verification bias had slight effects on test accuracy. There were 224 deaths, with a strong gradient between PET stage and death (P<.001).

Conclusion  The diagnostic accuracy of PET for assessment of suspected lung cancer is substantially affected by verification bias.

Author Affiliations: Departments of Cardiovascular Medicine (Dr Lauer), Thoracic and Cardiovascular Surgery (Drs Murthy, Blackstone, Okereke, and Rice), and Quantitative Health Sciences (Drs Lauer and Blackstone), The Cleveland Clinic, and Department of Epidemiology and Biostatistics, Case Western Reserve University (Dr Lauer), Cleveland, Ohio.

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