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Light has been responsible for defining many aspects of the classification of pleural effusions. However, we thought that his editorial¹ on tuberculous pleuritis confused the statistical terminology. In the editorial, Light comments on test specificity but actually describes positive predictive value. Sensitivity and specificity are properties inherent to the test itself and are usually considered to be independent of prevalence. This independence may not be completely true in practice, since the disease severity in patients whose results are selected to demonstrate the sensitivity and specificity of a test may be different than that typically encountered (spectrum bias).² However, the predictive value (both positive and negative) of a test is highly dependent on the prevalence of disease. This can be demonstrated using 2x2 tables with the test characteristics described by Light.

Table 1 reproduces the conditions of disease prevalence of 1%, a false-positive rate of 10%, and a sensitivity . . . [Full Text of this Article]

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Establishing the Diagnosis of Tuberculous Pleuritis
Richard W. Light
Arch Intern Med. 1998;158(18):1967-1968.
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