BMJ 2001;323:1188 ( 17 November )

Letters

Systematic reviews of evaluations of diagnostic and screening tests

    Odds ratio is not independent of prevalence
    Two issues were simplified

Odds ratio is not independent of prevalence

The first 150 words of the full text of this article appear below.

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 high risk. A diagnostic odds ratio of 10.00 in a low risk population may represent a very weak association between the experimental test and the gold . . . [Full text of this article]
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Relevant Article

Systematic reviews in health care: Systematic reviews of evaluations of diagnostic and screening tests
Jonathan J Deeks
BMJ 2001 323: 157-162. [Extract] [Full Text] [PDF]

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