Endgames

Statistical question

Positive predictive value

BMJ 2009; 339 doi: 10.1136/bmj.b3835 (Published 23 September 2009)
Cite this as: BMJ 2009;339:b3835

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  1. Siva K Talluri, clinical assistant professor
  1. 1Mclaren Regional Medical Center, Flint, MI 48532, USA
  1. talluri1{at}msu.edu

    A 50 year old man presents with a sore throat. You suspect streptococcal pharyngitis and request a rapid streptococcal antigen test. The sensitivity of this test is 80% and the specificity is 95%. The prevalence of streptococcal pharyngitis in adults with pharyngitis is 10%.

    What is the likelihood that the patient has streptococcal pharyngitis if the rapid streptococcal antigen test is positive?

    • a) 64%

    • b) 80%

    • c) 95%

    • d) 98%

    Answer

    a—The likelihood that the patient has streptococcal pharyngitis if the rapid streptococcal antigen test is positive is termed the positive predictive value of the test. In general, the positive predictive value of any test indicates the likelihood that someone with a positive test result actually has the disease.

    Predictive values are useful to the clinician as they indicate the likelihood of disease in a patient when the test result is positive (positive predictive value) …

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