Letter

Systematic reviews of evaluations of diagnostic and screening tests

BMJ 2001; 323 doi: 10.1136/bmj.323.7322.1188a (Published 17 November 2001)
Cite this as: BMJ 2001;323:1188.2

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Odds ratio is not independent of prevalence

  1. Nicole Jill-Marie Blackman, senior biostatistician (nicole_blackman-1@gsk.com)
  1. GlaxoSmithKline, 1250 South Collegeville Road, PO Box 5089, Collegeville, PA 19426-0989, USA
  2. Department of General Practice, Academic Medical Centre, University of Amsterdam, 1105 AZ Amsterdam, Netherlands
  3. Department of Clinical Epidemiology and Medical Technology Assessment, Maastricht University Hospital, 6202 AZ Maastricht, Netherlands
  4. Horten Centre, University of Zurich, CH-8091 Zurich, Switzerland

    EDITOR—Deeks, in the third of four articles on evaluations of diagnostic and screening tests, promoted the odds ratio as often being constant regardless of the diagnostic threshold.1 We agree with Deeks's statement that the choice of threshold varies according to the prevalence of the disease. But the statement that the odds ratio is generally constant regardless of the diagnostic threshold can be misleading.

    The value of an odds ratio, like that of other measures of test performance—for example, sensitivity, specificity, and likelihood ratios—depends on prevalence.2 For example, a test with a diagnostic odds ratio of 10.00 is considered to be a very good test by current standards. It is easy to verify that this is generally true only in populations at …

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