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Article
May 8, 1987

Are All Significant P Values Created Equal?The Analogy Between Diagnostic Tests and Clinical Research

Author Affiliations

From the Departments of Medicine (Dr Browner), Pediatrics (Dr Newman), and Epidemiology and International Health (Drs Browner and Newman), School of Medicine, University of California at San Francisco, and the Clinical Epidemiology Program, Institute for Health Policy Studies, San Francisco (Drs Browner and Newman).

From the Departments of Medicine (Dr Browner), Pediatrics (Dr Newman), and Epidemiology and International Health (Drs Browner and Newman), School of Medicine, University of California at San Francisco, and the Clinical Epidemiology Program, Institute for Health Policy Studies, San Francisco (Drs Browner and Newman).

JAMA. 1987;257(18):2459-2463. doi:10.1001/jama.1987.03390180077027
Abstract

Just as diagnostic tests are most helpful in light of the clinical presentation, statistical tests are most useful in the context of scientific knowledge. Knowing the specificity and sensitivity of a diagnostic test is necessary, but insufficient: the clinician must also estimate the prior probability of the disease. In the same way, knowing the P value and power, or the confidence interval, for the results of a research study is necessary but insufficient: the reader must estimate the prior probability that the research hypothesis is true. Just as a positive diagnostic test does not mean that a patient has the disease, especially if the clinical picture suggests otherwise, a significant P value does not mean that a research hypothesis is correct, especially if it is inconsistent with current knowledge. Powerful studies are like sensitive tests in that they can be especially useful when the results are negative. Very low P values are like very specific tests; both result in few false-positive results due to chance. This Bayesian approach can clarify much of the confusion surrounding the use and interpretation of statistical tests.

(JAMA 1987;257:2459-2463)

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