Endgames Statistical question

Screening tests

BMJ 2009; 339 doi: https://doi.org/10.1136/bmj.b3941 (Published 30 September 2009) Cite this as: BMJ 2009;339:b3941
  1. Philip Sedgwick, senior lecturer in medical statistics
  1. 1Centre for Medical and Healthcare Education, St George’s, University of London, Tooting, London SW17 0RE
  1. p.sedgwick{at}sgul.ac.uk

    A new rapid urine test was evaluated as a screening tool for Chlamydia trachomatis infection in men.1 The test was compared with the gold standard diagnostic test for chlamydia infection—the polymerase chain reaction (PCR) assay. The rapid urine screening test was reported to have a sensitivity of 82.6% and specificity of 98.5%.

    Which of the following statements, if any, are true?

    • a) Diagnostic ability: The rapid urine screening test does not provide a diagnosis of chlamydia infection.

    • b) Definition of sensitivity: out of all of the men with a “positive” result on the rapid urine screening test, 82.6% had a diagnosis of chlamydia infection on the PCR assay.

    • c) Definition of sensitivity: out of all of the men with a diagnosis of chlamydia infection according to the PCR assay, 82.6% had a “positive” result on the rapid urine screening …

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