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  • Image not available.Selecting the appropriate diagnostic procedure depends, in part, on the clinician’s index of suspicion.
  • Image not available.The threshold model for testing contains two decision points: when the index of suspicion is high enough to order a diagnostic procedure, and when the index of suspicion is so high that results from a procedure will not influence subsequent actions.
  • Image not available.Two components of evaluating diagnostic procedures are sensitivity and specificity.
  • Image not available.Sensitivity is a procedure’s ability to detect a disease if one is present.
  • Image not available.Specificity is a procedure’s ability to give a negative result if no disease is present.
  • Image not available.Two errors are possible: false-positive results occur when the procedure is positive but no disease is present; false-negative results occur when the procedure is negative but a disease is present.
  • Image not available.Sensitivity and specificity must be combined with the clinician’s index of suspicion to properly interpret a procedure.
  • Image not available.The 2 × 2 table method provides a simple way to use sensitivity and specificity to determine how to interpret the diagnostic procedure after it is done.
  • Image not available.After sensitivity and specificity are applied to the clinician’s index of suspicion, the probability of a disease based on a positive test and the probability of no disease with a negative test can be found. They are the predictive values of a positive and negative test, respectively.
  • Image not available.A likelihood ratio is the ratio of true-positives to false-positives; it is used with the prior odds of a disease (instead of the prior probability) to determine the odds after the test is done.
  • Image not available.A decision tree may be used to find predictive values.
  • Image not available.Bayes’ theorem gives the probability of one outcome, given that another outcome has occurred. It is another way to calculate predictive values.
  • Image not available.A sensitive test is best to rule out a disease; a specific test is used to rule in a disease.
  • Image not available.ROC (receiver operating characteristic) curves are used for diagnostic procedures that give a numerical result, rather than simply being positive and negative.
  • Image not available.Decision analysis, often using decision trees, is an optimal way to model approaches to diagnosis or management.
  • Image not available.Outcomes for the decision analysis may be costs, quality-of-life adjusted survival, or subjective utilities measuring how the patient values different outcomes.
  • Image not available.The optimal decision from a decision tree may be analyzed to learn how sensitive the decision is to various assumptions regarding probabilities, costs, etc.
  • Image not available.Decision analysis can be used to compare two or more alternative approaches to diagnosis or management (or both).
  • Image not available.Decision analysis can be used to compare the timing for diagnostic testing.
  • Image not available.Journal articles should not publish predictive values without reminding readers that these values depend on the prevalence or index of suspicion.


Presenting Problem 1


A 57-year-old man presents with a history of low back pain. The pain is aching in quality, persists at rest, and is made worse by bending and lifting. The pain has been getting progressively worse, and in the past 6 weeks has been awakening him at night. Within the past 10 days ...

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