Table 6.2Terms and Notation Used to Calculate Predictive Value

Probability of disease: The physician's estimate of the patient's likelihood of having the disease before a diagnostic test is performed. Also termed the prevalence of disease, or prior probability of disease.p(D+)
Probability of not having disease: 1 − p(D+).p(D)
Test sensitivity: The probability that a test result will be positive among patients with the disease.p(T+|D+)a
Test specificity: The probability that a test result will be negative among patients without the disease.p(T|D)
Predictive value positive: The probability that a patient has the disease given a positive test result.p(D+|T+)
Predictive value negative: The probability that a patient does not have the disease given a negative test result.p(D|T)

The "|" bar indicates conditional probability; the parameter on the left of the bar being conditional on the right parameter. In this example it is the probability of being test positive in the group that has disease.

From: Chapter 6, Sensitivity, Specificity, and Predictive Value

Cover of Clinical Methods
Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd edition.
Walker HK, Hall WD, Hurst JW, editors.
Boston: Butterworths; 1990.
Copyright © 1990, Butterworth Publishers, a division of Reed Publishing.

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