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Diagnostic and prognostic test assessment in emergency medicine: likelihood and diagnostic odds ratios
  1. Keith A Marill
  1. Emergency Medicine, Massachusetts General Hospital, Boston, Massachusetts, USA
  1. Correspondence to Dr Keith A Marill, Emergency Medicine, Massachusetts General Hospital, Zero Emerson Place, Suite 3B, Boston, MA 02114, USA; kmarill{at}


Emergency physicians use diagnostic and prognostic tests on a daily basis to assess for life-threatening illness and to inform clinical decisions. Current and new tests must be scientifically evaluated for their diagnostic utility. We discuss the evaluation of diagnostic and prognostic tests using the Bayesian likelihood ratio (LR) and logistic regression diagnostic odds ratio (OR) frameworks. These approaches can be applied to a single test in isolation using univariate techniques, or to a group of tests as commonly applied in clinical practice using multivariate methods. We compare and contrast the relative benefits and challenges of the LR and OR approaches, and assess their interchangeability. The concepts of diagnostic multivariate testing also underlie the framework of clinical decision rules which have gained acceptance in emergency medicine. Clinical decision rules can be viewed as a subanalysis within the joint LR framework. Ultimately, a variety of approaches may be acceptable and even complementary to assess a diagnostic test, each with its own merits and limitations.

  • diagnosis
  • methods

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  • Handling editor David Metcalfe

  • Contributors KAM conceived and wrote the manuscript in its entirety.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.