Arthur T. Evans, MD, MPH
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Evans AT. Subgroup Variation in Diagnostic Test Evaluation. Ann Intern Med. 2003;138:686. doi: 10.7326/0003-4819-138-8-200304150-00023
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Published: Ann Intern Med. 2003;138(8):686.
TO THE EDITOR:
The article by Mulherin and Miller on subgroup variation in diagnostic test evaluation is an important contribution (1). Although test performance may truly vary across subgroups, this variation might also be spurious—reference test bias masquerading as spectrum effect.
Whenever the reference test—the gold standard—is imperfect (a common occurrence), test characteristics (sensitivity, specificity, and likelihood ratios) will vary across subgroups that differ in prevalence of disease (2-4). Sensitivity will spuriously appear higher and specificity will spuriously appear lower in the patient subgroups with the higher prevalence, merely because the reference test is imperfect. This pattern assumes that the errors of the test and the reference standard are independent; if not, then the variation of sensitivity and specificity with prevalence can have a different pattern.
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