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Case–Control and Two-Gate Designs in Diagnostic Accuracy Studies

Departments of¹ Clinical Epidemiology and Biostatistics and ³ Urology, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.
² Department of Clinical Epidemiology, Leiden University Medical Center, Leiden, The Netherlands.

^aAddress correspondence to this author at: Department of Clinical Epidemiology and Biostatistics, Academic Medical Center, University of Amsterdam, Location Code J1b-210, PO Box 22700, 1100 DE Amsterdam, The Netherlands. Fax 31-20-6912683; e-mail a.rutjes{at}amc.uva.nl.

Abstract

Background: In some diagnostic accuracy studies, the test results of a series of patients with an established diagnosis are compared with those of a control group. Such case–control designs are intuitively appealing, but they have also been criticized for leading to inflated estimates of accuracy.

Methods: We discuss similarities and differences between diagnostic and etiologic case–control studies, as well as the mechanisms that can lead to variation in estimates of diagnostic accuracy in studies with separate sampling schemes ("gates") for diseased (cases) and nondiseased individuals (controls).

Results: Diagnostic accuracy studies are cross-sectional and descriptive in nature. Etiologic case–control studies aim to quantify the effect of potential causal exposures on disease occurrence, which inherently involves a time window between exposure and disease occurrence. Researchers and readers should be aware of spectrum effects in diagnostic case–control studies as a result of the restricted sampling of cases and/or controls, which can lead to changes in estimates of diagnostic accuracy. These spectrum effects may be advantageous in the early investigation of a new diagnostic test, but for an overall evaluation of the clinical performance of a test, case–control studies should closely mimic cross-sectional diagnostic studies.

Conclusions: As the accuracy of a test is likely to vary across subgroups of patients, researchers and clinicians might carefully consider the potential for spectrum effects in all designs and analyses, particularly in diagnostic accuracy studies with differential sampling schemes for diseased (cases) and nondiseased individuals (controls).

The following articles in journals at HighWire Press have cited this article:

				B. H Willis Spectrum bias--why clinicians need to be cautious when applying diagnostic test studies Fam. Pract., October 1, 2008; 25(5): 390 - 396. [Abstract] [Full Text] [PDF]

				M. Leeflang, J. Reitsma, R. Scholten, A. Rutjes, M. Di Nisio, J. Deeks, and P. Bossuyt Impact of Adjustment for Quality on Results of Metaanalyses of Diagnostic Accuracy Clin. Chem., February 1, 2007; 53(2): 164 - 172. [Abstract] [Full Text] [PDF]

				A. W.S. Rutjes, J. B. Reitsma, M. Di Nisio, N. Smidt, J. C. van Rijn, and P. M.M. Bossuyt Evidence of bias and variation in diagnostic accuracy studies. Can. Med. Assoc. J., February 14, 2006; 174(4): 469 - 476. [Abstract] [Full Text] [PDF]